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Between Silk and Cyanide

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Illustrated with photos. Twenty-three is awfully young to find yourself with the power of life and death. . . Leo Marks failed the examination to go and work on codes at Bletchley by being just too good and too much of a smart aleck. Instead, he was imposed on a not entirely willing Special Operations Executive (SOE) to teach coding to agents dropped into Europe and to decode the sometimes indecipherable messages they sent back at great risk to their lives. His speeches to his staff on the mortal danger of slowness or carelessness are classics of guilt-tripping. Absence of mistakes made him suspect that the Germans had captured SOE's Dutch agents--his youth and personality meant that his superiors were slow to believe him. In his spare time, he revolutionized cryptography by inventing one-time-only pads, and wrote poems for agents to use as keys--including the poem associated with Violette Szabo, "Odette".

This is a moving memoir of the agents like Odette and Noor Inayat Khan, whose fates we already know and whom he tried in vain to protect. This is a powerful memoir of war, responsibility and guilt; Marks, hitherto famous as screenwriter on Peeping Tom and son of the 84 Charing Cross Road family, has written a classic. --Roz Kaveney

416 pages, Hardcover

First published June 12, 1998

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Leo Marks

6 books10 followers
Leo Marks was a British playwright also famous for his cryptography work.

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Displaying 1 - 30 of 314 reviews
Profile Image for K.J. Charles.
Author 65 books12.1k followers
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October 18, 2024
The memoir of SOE's head of codes. Marks was 22, spoiled rotten, bursting with attitude, and a genius cryptographer. I'm not a zillion per cent sure I believe everything in this book (it's big on detailed recollections of conversations, poems, clothing, movements etc from fifty years ago) but in the round it's a remarkable read. The author's frequent expressions of humility and self doubt in no way disguise that he is massively full of himself, but then, he deserves to be. And what rings absolutely true is his feelings about being a 'backroom boy' while others went off to face appalling physical danger, the horror of watching them go, the greater horror of realising the backroom was failing them. Well written and fascinating.
Profile Image for Rose.
401 reviews52 followers
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September 14, 2009
This is a fantastic book. It is gripping, educational, and funny, and comes highly recommended.

At the age of 22, Leo Marks joined the Special Operations Executive, which managed resistance, espionage, and sabotage operations in Occupied Europe. His path to becoming an SOE cryptographer was not particularly smooth. First off, his interview with the code-breaking school did not get off to a good start, when the interviewer:

...began the interview by asking what my hobbies were.
"Incunabula and intercourse, sir."
It slipped out and wasn't even accurate; I'd had little experience of one and couldn't afford the other.


Having been accepted, he then became the only member of his class not to be considered worthy of the main cryptographic agency, Station X at Bletchley Park - mainly because of a bad case of being too clever for his own good. He was offered to SOE, but was very nearly rejected after they asked him to "break" an encoded message and were most disappointed when this took him the best part of a day, noting that their girls could do it in 20 minutes. Dismissing him, the captain asked for the code back, and was rather shocked to find out that Marks had not actually had the code, and had not expected one since they asked him to "break" rather than decode the message. And this was a code that they were actually using operationally.

Unfortunately, the rest of their codes and procedures were about as secure, and equally disrespectful to the lives of the people who depended on them. This is what made the book so moving, for me. Many of the power-wielding paper-pushers in London were far more preoccupied by petty politics than by whether or not their workers behind enemy lines lived or died.

I was saddened and angered by the needless sacrifice of those courageous people who volunteered for such dangerous work - knowing full well that if they were caught, they would be horribly tortured and then killed or sent to die in an extermination camp.

The main theme throughout the book is Marks' urgent efforts to improve matters. Unlike many of those in power in SOE, he seems to have been constantly aware that codes were not just paper exercises, and made a nuisance of himself throughout his work there by trying to change how cryptography was handled. His eventual success in doing so was considerable, but came far too late for many who died at the hands of the Gestapo.

Yet Marks never gave up, even though he often had to go outside official channels or use unorthodox means to do so - frequently with somewhat amusing results - whether frisking officials, impersonating his boss in memos, or bribing people with black-market provisions acquired by his mother. For example, he becomes so frustrated by the unwillingness of SOE to help him recruit more women for his Codes division that he sends a message to the Ministry of Labour: "Do not reject any girl on grounds of insanity without first offering her to SOE."

However, the reader never forgets - and is, without preaching, never permitted to forget - the deeply serious business veiled over by actions that at the time were more desperate than amusing.

A large part of the problem was the politics and infighting rife within SOE, and between it and other agencies (especially "C", the Secret Intelligence Service). The whole situation was aptly described by one of SOE's spies (who "couldn't wait to return to the peace and quiet of occupied France") as "a f**king mad hatter's tea party". Marks at least becomes adept at using these rivalries to his advantage: when agents or sections are reluctant to adopt his coding innovations, he regretfully informs them that he might not have enough for them because the Free French, or whoever, were getting priority.

One of Marks's main preoccupations throughout the book is Holland. Based on their messages, Marks believed that most or all of SOE's agents there had been captured, with their messages sent under duress or directly by Marks's nemesis, Herr Giskes. For the most part, SOE refuses (you will be surprised to learn) to take Marks seriously despite the evidence piling up, and continues to send stores and agents straight into the hands of the Nazis. Largely powerless to change this situation despite his strenuous efforts, Marks institutes Plan Giskes to salvage what he can from the sorry mess.

A vital component of this was his efforts to lull Giskes into a false sense of security for when the plan got underway. His code-briefing to a team about to be dropped into Holland (and almost certainly captured by Giskes) has a secondary aim:

In basic terms, the ideal impression they would convey to him was that I seemed inexperienced, uninspired, and whatever the Dutch was for a bit of a c**t. The high master of St Paul's had frequently expressed this in Latin in my end-of-term reports, and I was about to demonstrate just how right he had been.


Of course, since Marks is the book's author, the reader naturally has to consider this source of potential bias, especially concerning his own role. I found, however, that I had a high degree of trust in Marks and in the way he related events. He does not cut himself any slack while pointing out the weaknesses of others, as the quote above suggests. Indeed, he is relentless in pursuing and taking responsibility for his mistakes. Probably aware of how ludicrous it would be to take oneself too seriously in a climate in which the most serious matters are treated so lightly, Marks never misses an opportunity to skewer his own failings.

The captain who instructed me was so full of himself that I spent the entire session trying to determine the reason for his self-esteem and failed to take in a single word of his instructions, except for "Any questions? Right. Get on with it."


Between Silk and Cyanide is a remarkable book that will stay with me for a long time. Marks' writing style is fresh and vivid. He sounds just like the young man he was at the time, with little hint of the intervening years. My only, minor, criticism is that I would have liked more explanation of how the main codes worked, albeit simplified (I suspect that an editor may have taken these bits out on the grounds that they were too technical, but it means that other technical explanations make no sense - I re-read parts several times trying to work out what I'd missed and why I didn't understand, before realising that the information wasn't actually there and resorting to the Internet). It's a deeply human and affecting story - and one with a fine sense of the ridiculous.
Profile Image for Anne .
459 reviews464 followers
September 15, 2021
What a fascinating read. This book is about the use of cryptanalysis by British secret agents sent to Europe during WWII and the people in London, particularly Leo Marks, who trained these agents and received their encrypted messages from all over the world. You might think that a book about cryptanalysis would be very dry. Well, this one is not dry at all. Leo Marks is a very gifted storyteller and writer. As interesting as the cryptanalysis is, and particularly Marks' efforts to make it safer, it is the human stories that are so compelling and gripping in this book.

I've read many books and seen many movies about WWII and the resistance in France and elsewhere. At some point there is usually an agent sending coded messages to London. Often there are scenes in which the Gestapo is honing in on the coder’s radio signal location while he/she is transmitting. Often the signal operator is captured. This book is about these agents and the people in London who received and decoded their messages. I learned why the radio operator had the most dangerous job in the resistance and was in awe of the bravery and self-sacrifice of the people who volunteered for these clandestine missions.

Marks spent the entire war trying to make radio transmission safer and more secure. One of his inventions was the use of silk on which to write codes, silk being easier to hide in the seams of clothes and elsewhere while crossing dangerous checkpoints and to burn after use. At one point in the book Marks is asked to explain why his invention of writing codes on silk should be adopted. His reply: “It can be reduced down to a single phrase. It's between silk and cyanide,” cyanide being the pill that each agent carried with them in order to be taken in lieu of being captured and tortured (and possibly giving away names and locations of other agents). Hence, the title of this book.


Marks failed the Bletchley Park entrance test due to his snubbing of authority and his precocious insistence on finding shortcuts to deciphering codes instead of decoding the way he was taught. These qualities came in handy after he was scooped up by a new secret ogranization, Special Operations Executive (SOE), designed to train agents for sabotage missions of the Axis war efforts in occupied Europe and to aid local resistance movements.

Within a short period Marks' brilliance as a cryptographer became apparent and he soon became the head of Cryptography, running all coding training and decoding operations. It was thrilling to read Marks' stories about teaching coding to agents I've read about elsewhere, Yeo Thomas, Vera Atkins, Noor Inayat Khan, Violette Szabo to name a few. Following their fates and the fate of other agents made for gripping reading.

Learning about Marks' experiences decoding messages from agents all over the world was also fascinating. I was amazed by how many "indecipherable" messages were sent and the reasons they required hours to decode. One of the saddest parts of the book is about the agents who were caught by the Germans. The story about the agents sent to Norway after their network had been infilitrated by the Germans is the saddest and most maddening (and left a black mark on SOE’s operations for posterity). Marks figured out early on that the messages coming from Norway were not being sent by the English agents or, if they were, it was under duress. Agents had been taught to drop their security check codes as a signal to London if they were ever caught and forced to send messages to London. All of the messages coming from Norway not only had no security checks but were also always perfectly coded. Even the best coders never had perfectly coded messages all of the time, either in training or in the field. Marks was convinced that these messages were being sent under duress but his warnings to his superiors fell on deaf ears and for months Marks had to watch more and more agents being sent in to Norway. During this time Marks continued to communicate with Norway. Eventually, two captured agents escaped, made their way to Switzerland and got a message through to London with the “news” that the Norwegian network was compromised. Altogether, 50 agents were sent to Norway along with tons of supplies. Almost all of these agents were captured and killed. The top brass at SOE suppressed this knowledge. 50 years after the war Marks set the record straight with the writing of this book.

So, with whom was Marks communicating in Norway? A German Colonel, Hermann Giskes. Once it became clear to Giske that he'd been discovered he sent the following chilling, unencrypted message to London/Marks:


"To [the SOE section chiefs, London. In the last time you are trying to make business in Netherlands without our assistance stop we think this rather unfair in view of our long and successful co-operation as your sole agents stop but never mind whenever you will come to pay a visit to the Continent you may be assured that you will be received with the same care and result as all those who you sent us before stop so long."

At the end of the war Giske wrote his own book about his experience: “[book:London Calling North Pole|2020249].”

I couldn't give this book 5 stars because of some issues I had with the book. When Marks was writing about the technical side of code making and breaking my brain stopped attending. That's not his fault but for my taste there was too much technical talk. Much of this book, particularly the second half, is very suspenseful and made me want to laugh and cry at the same time. The humor comes from Marks himself though he uses it way too much and is often snarky and ironic and not in a good way. Last, Marks was 22 years old when he was hired by SOE. His ability to tell a story and to oversee Cryptology were all quite brilliant. But his false self-deprecation and smugness were off-putting.

As I mentioned above, Marks is a talented writer. After the war he moved on to writing successful screenplays, plays and poems. He also wrote poems during the war. One of these he wrote for his girlfriend right after she died in a plane crash:

The Life That I Have

The life that I have
Is all that I have
And the life that I have
Is yours.

The love that I have
Of the life that I have
Is yours and yours and yours.

A sleep I shall have
A rest I shall have
Yet death will be but a pause.

For the peace of my years
In the long green grass
Will be yours and yours and yours.


Marks later gave this poem to one of his agents, Violette Szabo, to use for her coding (and also because he'd fallen a little in love with her when they met). The Life That I Have was later made famous by the book and 1958 movie about Szabo, both named Carve Her Name with Pride.

I listened to the audio version of this book. The narrator, Eric Martin, was superb.

If the name "Marks" sounds familiar that's because Leo Marks' father was the co-owner of Marks and Co, an antiquarian book shop at 84 Charing Cross Road. This address and bookstore were made famous by the book (and later the movie) 84, Charing Cross Road by Helene Hanff.
Profile Image for A.L. Sowards.
Author 22 books1,225 followers
November 19, 2013
I added this to my to-read list last year, when a goodreads friend (thanks, Christie!) said it was among the best WWII books she’d read in 2012. Now that I’ve read it, I have to say that it’s among the best I’ve read in 2013.

The book begins with Leo Marks going off to war—to codebreakers school. He spends too much time trying to find shortcuts, so his instructors decide he’s not quite good enough for Bletchley Park (where the British are busy breaking German codes), but maybe a new outfit called SOE can use him. On his first day, he’s given a coded message and told to decode it. Everyone seems to think he should be able to accomplish his task within a half hour, so when it takes him until tea-time, he’s convinced he won’t be asked to stay. As he’s slinking from the room, someone asks him to leave the code.

“What code, sir?”

. . . “The code you broke it with!”

“You didn’t give me one, sir.”

. . . “How did you decode that message if I didn’t give you one?”

“You told me to break it, sir.”

. . . “You mean you broke it . . . without a code?”


So begins Marks’ SOE career. He’s eventually put in charge of agents’ codes, and spends the war trying to make them more secure. Marks doesn’t fight on the front lines and he never enters Nazi-occupied territory, but he has his battles. Some of them are with rival British intelligence organizations. Others are spent trying to convince the bureaucracy that the old coding systems aren’t secure and that the traffic coming from Dutch agents is highly suspicious. In a memorable moment, he tells the Free French (who were usually at odds with the British French section run by Buckmaster) that he doesn’t care if the French agents vote for or against de Gaulle after the war, as long as they’re alive to vote at war’s end.

Marks is young during the war, in his early twenties. He can’t tell his doting parents or their friends what he’s really doing. Several anonymous acquaintances send him white feathers throughout the war, assuming he’s a shirker. The long hours trying to break codes and get needed materials when everything is in short supply wear on him, as do the deaths and other mishaps in the field. Perhaps because of his age, his frequent unauthorized actions, and the personal growth Marks experiences, the book had a slight coming-of-age feel to it.

The writing is excellent. It’s a memoir, and Marks wrote plays and screenplays post-war, so he has an eye for a story. I laughed out loud nearly every chapter, which is kind of rare in a history book. The information is interesting—covering numerous aspects of WWII, but from a different angle than what I’ve read before. The only thing I would have liked better is a more complete epilogue. I guess I’ll have to go find books on Yeo-Thomas and the Grouse team and some of the other agents who wandered through the pages to learn more details of their missions and their lives post-war.

Highly recommended if you have any interest in WWII intelligence operations. It may also interest readers who simply enjoy British humor.
Profile Image for Meaghan.
1,096 reviews25 followers
September 14, 2012
I admit that all the jargon about codemaking and codebreaking went over my head, but Marks's self-deprecating humor and engaging writing style kept me going so I finished the whole book in just two sittings in less than 24 hours. People who like World War II books will love this -- it's thrilling and suspenseful but without the violence. I did not envy the coders, and even less so the field agents, and I admired Marks for kicking and screaming and agitating so much to try to make their lives easier (and longer).

Bonus: I wrote an Executed Today entry for Noor Inayat Khan, one of the more memorable characters I first encountered in Between Silk and Cyanide.
Profile Image for Jeanette.
4,081 reviews838 followers
December 21, 2014
Worth the detailed read about code breaking by SOE during WWII years for those who have patience and interest because it is dense reading. How the organization formed and what components melded during the get-go under Great Britain's distress were exceptional.

But this will appeal far more to people who love logic puzzles or maybe difficult math progressions. Because there is majority explanation in those pattern abilities here; enough which would make people who don't enjoy math go cross-eyed.

For me, it could not be a 4 star because I find Leo Marks egotism annoying. His humor has aspects that I tend to loathe, as well. The other characters of intersect around SOE/Marks (especially the wireless operators) I've read about in other non-fiction: they were of immense interest to me. When he leaves them on center stage the book is better, but Marks just knocks them out of the box most of the time by patting himself on the back during the over story.

If you like puns, ridicule, snarky snide and "aren't I the clever one" hubris AND code forms- then this one may be a 5 star for you.
Profile Image for Zora.
1,342 reviews70 followers
August 17, 2016
What is it about the story that keeps me coming back to it? The story of how Hitler was defeated, especially the role of the French underground and British spies and regular English girls doing amazing things on the homefront, this to me is the greatest story ever told and likely always will be. Funny, touching, intellectually stimulating, here is a terrific addition to that powerful tale.

The title refers to the conversation had, when the author was asked why meager stores of silk should be used to print out code keys. "The choice is between silk and cyanide," he said. That is, you do this, or more agents will have to take their L pill of cyanide.

It was about page 25 that I realized who this guy was , when his first reference to poems hit home for me. I'd just seen, and sobbed my way through, Carve Her Name With Pride this year, and I knew from after-movie research that the real source of Violette's poem was the SOE codemaster... Marks. I thought, oh dear, I'm going to have to get all weepy over that again. Indeed I did have to, but also I got new people to cry about, Noor and Tommy. Do we have it inside us any more to be that courageous? Most days, I fear we have lost the knack.

I like Marks's self-deprecating humor and disobedience to authority. His intelligence shines through. (When a commander Hogg gives the 22-yr-old author the anti-Semitic gimlet eye and asks "is that Marx with an 'x'? Leo shoots back, "is that Hog with one "g"? )

After reading this, I hunted down more info online, and found some jewels, including Tommy's farewell letter to his commander, smuggled out of the Nazi death camp. Great stuff, and there is more yet to read.
Profile Image for Steve Merrick.
Author 16 books8 followers
November 19, 2011
I was despairing when I finally reached this gem of a book. Its one of the nightmares when you are researching subjects like Special Operations Executive, (British wartime organization with the brief from Churchill to set Europe Ablaze! sending agents hither and dither across Europe the SOE did just that.) There is a dearth of books mostly bad written about it, Yet before I get side tracked by that, I can say that this is one of the funniest and thought provoking books about espionage that I have ever read, even the title makes sense when you read the book and it is satisfying to break the codes and clues left for you.

Of the Little bleeder that wrote this I can only offer the two words, "Respect Buddy!"

It starts hysterically then picks up steam, its a big book to, nearly six hundred pages of pure and gorgeous griping and it is an illuminating snapshot of one mans struggle with a crippling wartime bureaucracy. Unlike any of the other books on SOE I have read, Leo Marks can write beautifully and illustrates his odd view from the inside out of SOE, having the advantage of being there it is an illuminating bit of work.

Listen if I had more than five minutes free I would write a larger review but since I don't I have to just cut this one short and say quickly....

Read it Read IT Read it!!!!

If only for the fact that the master race and Hitler were often the least of Leo Marks worries......

I would give it ten out of Five stars but it would take a cryptographer to figure out how to do it.....


Profile Image for Alger Smythe-Hopkins.
1,096 reviews171 followers
May 22, 2014
A deeply frustrating book, one that falls very short of the inside history of a hidden war that that it promises, and is instead a personal memoir of a very vain and unreliable narrator.

Marks' greatest failing as a writer of memoirs is his false modesty, where he depreciates himself endlessly as a young a foolish boy whose only saving grace is his willingness to sacrifice his own best interests for the sake of the agents. Marks' greatest failing as a historian is his remarkable memory of events that passed 50+ years before, where he is the only surviving witness and all of the records of his office were destroyed soon after the war. The result is a book built upon the merry tale of a feckless English lad matching wits with the coolly professional German warmasters (and Gosh! He Wins!).

Then there is the problem with the framing of this narrative. To really follow what is happening as the author moves from event to event (in a loosely chronological sequence) one needs to have more than a passing knowledge of the British command structure, the British and German Intelligence Services, the timing of various battles and most of all, get a firm handle on the partisan politics of the many Governments in Exile and their guerrilla operations in occupied Europe. This isn't a singular failing of Marks, first person narratives are usually full of inside references and jargon. What is a problem is that the events described were already 50 years in the past by the time Marks got around to publishing this personal history, so really there is no excuse for all the inside jokes and gossip that Marks tries to pass off as colorful period detail. Marks' assumption that we already know what happened as well as he does, and his breezy writing style combined to throw me out of the story time and again while I tried to keep track of who he was introducing and their importance. Very often we are told that someone important is coming to visit him in his little office, and that this will change everything, and then nothing happens, and he never changes his behavior, and he never loses his utter certainty (no matter how much he claims to respect his superiors) that he is the only one in the entire war office who really really cares about the lives of the field agents. Neither was I given a reason to care about the people he claims to admire so much since he seems to believe that his own feelings and judgements are good enough for us to follow. That would only be possible if he hadn't spent so much time convincing us that his judgements are terrible and childish as part of his pose for the rest of the book.

Then there is the problem the reader has assessing exactly what Marks' contributions were to improving agent code security: how effective were his new codes?; were fewer agents captured?; was crucial information successfully passed? These are things we cannot even guess at because Marks is adept on the one hand of puffing up his various achievements (this is usually done though staged meetings with his superiors where their jaws either drop with astonishment with the wonders that he has revealed, or clench with anger at the damage he has done to their internecine battles with other intelligence divisions) while simultaneously telling us that they were mere bagatelles, a folly, a distraction, a stopping point on his way to an even better code product.

Then there are the poems. What the ?

Essentially, Marks is a fun and witty raconteur, who spins out a tale designed to make us admire his special genius without his seeming to brag. My suggestion is to read this book as a lightly fictionalized account of his experiences; think of Marks as just a guy you meet in the pub who is repaying you for endless drinks by spinning out the story of his life. It is long and gusty and unreliable and slightly heroic and full of dropped names and unlikely coincidences, but for the rest of your life you can tell people about this amazing character you met, and like as not you retell his stories word for word for word.

Profile Image for Nathan.
523 reviews4 followers
May 11, 2010
A bloated, blathering account of what should have been a fascinating subject. Marks's faults are manifold: he never gives us a clear picture of how he solved codes and leaves us in the dark for most of the book as to the exact significance of codebreaking in relation to the war effort as a whole. He's also rather full of himself, expecting us to be interested simply because being a codebreaker is Just So Cool!, and constantly making tired attempts at wit in order to leaven his dull account. 600 pages, and every one was painful.
Profile Image for Kay.
1,020 reviews217 followers
June 8, 2012
So far the author has spent an awful lot of time patting himself on the back for being so clever. I hope he stops soon or this will be shelved with the "50-page rule" books.

(Update, June 2012: I never did finish this, but got about halfway through. The insufferable smugness just wore me down, plus I tired of the minutia. - how the hell did he remember every detail and conversation? It seemed suspect. Perhaps he took incredibly detailed notes, which I assume was forbidden. No one could recall the kind of miniscule details he bores us with!)
Profile Image for Chris.
Author 18 books86 followers
November 17, 2012
If you love math, wordplay, puzzles in general, and tricks for navigating intense wartime bureaucracies, this book is for you. As for me, I was mainly interested because I recently learned that my great-aunt did coding during WWII. For me the most interesting parts were about the FANY (First Aid Nursing Yeomanry - who did espionage and many of whom were trained and supervised by the author) and stuff about how the war was won, and at what cost. While Marks' story was invaluable history, as a book it would have been more effective at half the length.
Profile Image for Christine.
7,213 reviews565 followers
December 31, 2017
Leo Marks worked in SOE during the Second World War, and this book is an account of what happened to him during that time. Marks writes with great humor (his father owned 84 Charing Cross Road), and sympathy. He is also respectful of the women he works with - doesn't look down on them acknowledges their intelligence. One of the funniest sections of the book has to do with monthies.

I just wish there had been years at the top of each chapter.
Profile Image for Zella Kate.
401 reviews21 followers
October 12, 2017
I've always been fascinated by cryptography and British espionage during WWII. (I blame repeatedly reading this book as a teenager: https://www.goodreads.com/book/show/1...)

I stumbled across a reference to Marks's book recently and was surprised I had never heard of it before. It's easily one of the best wartime memoirs I have ever read. Though Marks was, essentially, deskbound for the duration of the war, his account of his time developing codes for the SOE (a secret organization that instigated sabotage and organized partisan resistance movements against Nazi Germany) is every bit as gripping as a combat memoir.

Some of the cryptography stuff was beyond me, but overall Marks does a good job of explaining it to where you can follow along. He also has a delightful, self-deprecating, witty, and obscene British sense of humor. He excels at telling hilariously absurd stories, and there are a lot of them in here as he describes battling bureaucracy in his quest to increase the security of the codes assigned to his agents.

And that was no laughing matter. Marks clearly was fond of the agents in his care, and his affection for them and his sorrow at the ones who were lost is still palpable, though he wrote the book 50 years after the war. The sorest point for him--and the subplot I found most fascinating, though they were all interesting--was his cat-and-mouse game against his German counterpart in Holland, Hermann Giskes.

From the beginning of his time at SOE, Marks expressed concern about whether the Germans had infiltrated the Dutch SOE network. He felt like their wireless messages were too near and clean to be composed in the field, and he started to suspect that they were actually composed in controlled settings by the German intelligence service. Marks devoted a lot of effort into trying to prove this infiltration, but his superiors, though sympathetic, insisted that there was no way of knowing for sure whether he was right. As a result, they continued to send agents and supplies to Holland.

It was only after Giskes, in a real 1980s movie villain move, sent a taunting message to them that they realized that Marks had been right. And by that time, well over 50 SOE agents had been sent to their death in Holland. Little wonder Marks was so determined to ensuring his codes were secure and remained disturbed by the SOE's failures long after the organization ceased to exist.

Nevertheless, Marks never reads like he has an axe to grind--he's blunt about the SOE's shortcomings (and his own mistakes) but never to the point of being offputting.

Overall, one of the better, more unique books I've read all year.

Profile Image for Rachel.
971 reviews63 followers
November 28, 2008
Wow, this book was great! Eric's been trying to get me to read it for ages, and I finally got around to it.

Leo Marks was the cryptographer who revolutionized the British codes during World War II. He invented many of the codes used by the British during the war, briefed many of their agents, and organized systems for decoding "indecipherables" -- coded messages that were garbled to the point that they couldn't be decrypted. He also turns out to be an excellent writer (he's also a screenwriter and poet), and has written an intense, serious, and very human account of his experiences during the war. He has a sly sense of humor, keen insights, and tells many of the secrets he kept during the war (but one can be sure it's not all of them).

The motivation for the book seems to have been the doubt about whether the Dutch agents during the war were captured by the Germans, and for how long they had been compromised. Marks is able to answer that clearly, but points out that it was not acknowledged at the time for political reasons, and was never clarified after the war because those in the know were never asked. He takes this opportunity to set the record straight as he knew it.

His stories about the war are fascinating, illuminating, and frequently heartbreaking. This is a book well worth reading.
Profile Image for Cat..
1,918 reviews
July 5, 2015
Quite a funny book on a serious subject. He was involved in a major way with producing codes for Allied agents in Axis countries, outside of Germany & Italy, in Europe. Fascinating and frustrating. After the war, he became involved in making movies. Another odd connection is that his father was co-owner of the bookshop at 84 Charing Cross Rd. Now you know why I read that book. This one's better.
Profile Image for Jeffrey.
32 reviews2 followers
April 23, 2017
Take the cyanide -- it'll be more humane than reading this mess. If you care deeply about bureaucrtic intrigue in mid-century British intelligence agencies, laced with bad poetry, endless puns, inside jokes, false modesty, and a hazy explanation of cryptography, this is your book. I'd have never finished this unedited excuse for a memoir had I not paid for it. Let my pain be your salvation, and look elsewhere.
Profile Image for Tara .
508 reviews57 followers
November 13, 2018
A war memoir that somehow magically combines humor, intelligence, tragedy and triumph in one epic story. Leo Marks is a self-deprecating coding genius, who constantly pushed the envelope for what he believed was right and important, all for the sake of the lives of the agents whose codes he worked to decode and transcribe. This is a must-read for any WWII buff.
Profile Image for Faith Ann.
97 reviews2 followers
June 20, 2025
Like many nonfiction war novels, this book is heartbreaking. Somehow all these years later, armies still have bureaucracy issues and people won’t “play nice” when we’re on the same side - and this novel highlights the very real consequences of that in war with agents’ lives lost.

The author’s self-assuredness comes through and reads as cockiness sometimes, but it lent a very authentic feel to the story, even if I doubt his memory’s accuracy on some things all these years later (especially after reading The Optimism Bias, lol).

Highly recommend for anyone who’s into nonfiction war stories or WWII stuff! You don’t have to be able to fully understand the codes he introduces to be able to follow the book.
Profile Image for Charlie.
Author 71 books3 followers
August 23, 2018
A fascinating and captivating first hand account of WWII codes and coding from the person most responsible for them. Leo Marks was recruited into SOE after being rejected by Bletchley Park, but became responsible for both creating the codes used by British agents, and the decoding or deciphering of those agents messages, even when they weren't properly encoded. Between Silk and Cyanide gives a detailed account of the SOE's Signals division, and the creation of codes to allow their agents to communicate from within occupied territory.
Profile Image for Tom Leland.
412 reviews24 followers
March 21, 2020
Since it was a "national bestseller", and has plenty of 5-star reviews on Goodreads, there's obviously something great here for many -- not for me. I just couldn't get myself to give a damn about the minutia of the coding and the endless bureaucratic intrigue. He's got that brilliant Brit wit, though even that got tiresome. Starting skimming at around page 240.
37 reviews1 follower
April 7, 2013
This is a rare memoir, written with a unique voice. I've yet to reread Foot et. al. on SOE, but I intend to see just where Marx contradicts him. The destruction of evidence is one of the most shameful episodes in a long history of shame regarding SOE.

A number of things stand out: given that Marks presumably had ULTRA clearance, why wasn't he informed of the strategic ramifications of the code war until much later in the war? Given the several visits of SIS, it just seems odd they did not deign to brief him while bemoaning that he would not brief them. And we know subsequently that he did work in some advisory capacity for C.

An interesting comparison between Marks and R.V. Jones comes with the story of Thomas Sneum. At first glance, Marks' version seems to almost contradict Jones' but it is difficult to tell whether Jones was given the complete picture or chose/was forced to choose to abbreviate it, since it would expose the machinations of MI6 of which he was nominally a member. And given Jones' own attitude to agents and bureaucratic warfare, it's hard to credit that he would be less infuriated by the clash as Marx.

Finally I want to address a couple of points raised about the cryptanalysis in the book in other reviews. The book doesn't pretend to be an exhaustive explanation even of double transposition, so it can't be expected to be understood technically. At the time, most cryptanalysis was pre-mathematical and pre-algorithmic. Friedman's work was practically unknown outside US Army circles. Even Marx, with the resources of a rare bookshop would have been hard-pressed to find anything in public literature of much use prior to the 1950's. The practically canonical overview is David Kahn's The Codebreakers and Helen Gaines' Cryptanalysis A Study of Ciphers and Their Solution goes into the details of classical ciphers. Even a toy transposition cipher like Playfair was not attacked mathematically until much later because the analogue "algorithms" like anagramming already existed.

In fact, specific computers were invented to deal with the challenges presented by cipher machines, but the theory behind them was as tight a secret as ULTRA itself. It was only at this point that mathematics was engaged with cryptanalysis in the Bletchley war on Enigma and Fish and extended to simpler ciphers. But none of that information seems to have filtered over to Marx in any case; again, SIS wanted his results but were very parsimonious with their own.

Of greater value (to me) is the human story of this book; how the relentless pressure ground down a young man to the point he couldn't contemplate working as a cryptographer for longer than the war itself. How tragic and heroic his pupils were, and the stunning gift of his poetic imagination versus the implacable war machine he assisted.
Profile Image for Pedro.
91 reviews
March 4, 2015
Between Silk and Cyanide was a wonderful recommendation I received and it really paid off. When you think about cryptography during WWII the names that come to mind are Bletchley Park and Alan Turing, but Leo Marks did a fantastic job too. He describes his battle with the bureaucracy to provide better codes to the agents on the field in a very humorous tone, also he writes very well and the book is very agreeable to read.

My only regret is not having discovered this book while my grandpa was still alive a few years ago. He worked for 40 years as a WT operator and there are several morse code issues the book discuss and he would love to talk about it, in fact I learned morse from him. The last time we met he showed me a poem he wrote to his wife (my grandma) using morse code.

Even if you are not into cryptography you will enjoy this book. However if the cryptography bug infects you I'd suggest other two good books one non-fiction The Code Book: The Science of Secrecy from Ancient Egypt to Quantum Cryptography from Simon Singh, and other a spy novel from Robert Littell which has as main part of the plot the "Baconian theory of Shakespeare authorship" and the Bacon's Cipher: The Amateur.

I'm grateful to the author of Arriving at Amen: Seven Catholic Prayers That Even I Can Offer , Ms. Leah Libresco, for the recommendation of Between Silk and Cyanide.

P.S.: (have fun and crack, not so hard...!)

P.S.2: In case someone get desperate for an answer of the above puzzle.
Profile Image for Ensiform.
1,514 reviews148 followers
April 29, 2012
The author, at twenty-three, became head of codes at the Signals branch of SOE (Special Operations Executive) and changed the way the British ran codes. When he arrived, they were using poems a basis for their character transposition, a process that was open to typos and was easily cracked if a few key words of the poem were deciphered and the phrase was well known. Regarding the typos, Marks impressed his superiors by insisting that indecipherable messages would be cracked at SOE, without asking the agent in the field to take the risk of resending a new message. Hating the poem codes in general, he doggedly pushed against the bureaucracy who balked at all change, arguing for a system he called WOKs, for Worked Out Keys, and inventing what he called LOPs, or Letter-based One-time Pads, both of which could be used once and then destroyed. He also innovated the printing of codes onto the titular silks, which are easier to hide than paper.

From page one, Marks jumps right into the story, bringing only the bare minimum of relevant biographical details, which is refreshing. He’s a smart and funny narrator with a flair for puns and self-deprecating humor, which he manages to maintain over 600 pages without it becoming tiresome. But he knows how to tell a story, too. The main drama in the book is the Holland section, which Marks suspects has been compromised very early on due to their too-perfect coding. He cannot convince his obdurate employers, and he sees with chagrin agent after agent, and secret after secret, fall into the hands of the Germans who are maintaining the charade of communication with SOE. Finally, he takes matters into his own hands, and even if, as in fiction, there’s no dramatic act of closure, the way in which he works without the consent of his superiors to set a trap for the Germans is quite admirable. It’s a very well done memoir, and even if much of the coding went over my head, I found that as a record of how the British intelligence service operated in WWII, it’s hugely instructive as well as entertaining.
Profile Image for Michelle Diener.
Author 53 books1,921 followers
September 4, 2012
This is quite frankly the best book I have read in months and months. An auto-biographical account by Leo Marks of his time as the Head of Codes for Special Operations Executive, the British war department created to 'set Europe ablaze' during WWII, it was unputdownable.

That everything actually happened made the story even more riveting. I have always been interested in codes and ciphers, and I found Mark's descriptions of how they created codes and how they broke them fascinating. Marks is such a wonderful writer, he'd probably write a gripping account of how to watch paint dry, but with material like unearthing which Dutch agents had been captured by the Germans by analyzing their coded messages to headquarters, the in-fighting between SOE and the British Secret Service, as well as the ingenuity of Marks and other SOE operatives in laying their hands on scarce resources to do their jobs, I was reading late into the night three nights in a row.

Marks' wonderfully rich phrases and his dry, sardonic wit mean that even serious, sometimes heartbreaking situations are tackled with empathy and humour. His style shows his deep respect for the sacrifices of the agents who went into Occupied Territories to disrupt the German supply lines and organize insurgent armies.

Marks was the person who came up with the idea of printing codes on pieces of silk which could be burned after every use, hence the title of the book. Each agent was given a cyanide tablet to chew should they be captured, so the Nazis could not torture information such as codes out of them. When asked to come up with a two page report motivating why his silk system should be adopted rather than the very unsafe system they were using, Marks said: 'It can to reduced down to a single phrase. It's between silk and cyanide.'

I cannot recommend this book highly enough. Amazing writing, gripping story, totally compelling.
Profile Image for Jamie Collins.
1,556 reviews307 followers
August 19, 2014
A fascinating memoir by WWII cryptographer Leo Marks, the son of one of the owners of the Marks & Co antiquarian bookshop made famous by Helene Hanff’s book 84, Charing Cross Road (a nice read for bibliophiles). At the age of 22 Marks was deemed unsuitable for Bletchley Park due to his “originality” and flippant sense of humor (much in evidence in the book) and was sent to work for the Special Operations Executive instead, where he supervised encoded messages to and from intelligence agents in the field.

The book has a narrow focus and is mostly concerned with two of Marks’s most urgent goals, and it’s astonishing to read about the inter-departmental rivalries which hindered these goals and risked or wasted the lives of heroic field agents.

The first was to replace the alarmingly insecure poem codes used by agents with safer methods, including “worked-out codes” which would be printed on silk for agents to carry. (Silk is easy to hide in clothing - it won’t rustle during a pat-down search.)

Marks’s second goal was to convince his superiors that many, if not all, of the Dutch agents had been captured and their messages were in fact being manufactured by the Germans. He became suspicious because messages from the Netherlands had a markedly low rate of coding errors.

Marks does a nice job of explaining the basics of the cryptography. Much of his name-dropping passed me by due to my unfamiliarity with the famous WWII intelligence agents, and occasionally I would be mystified as to the point of one of his anecdotes, presumably again because of my lack of knowledge. I was nonetheless riveted by the story and entertained by his self-deprecating humor. I particularly enjoyed his references to his father’s bookstore, called only “84”.
286 reviews
June 12, 2021
This was the funniest thing I’ve read in months. The snark! The sarcasm! The PUNS!

I first learned about this book on the internet and thought I’d check it out, even though I know very little about cryptography and, you know, it’s 600 pages. So I put it on hold at the library, started reading, and was hooked.

First I found out on the first page that the author, Leo Marks, was the son of one of the owners of Marks & Co., the bookshop that Helene Hanff made legendary in her own book 84 Charing Cross Road (another five star read). So I kept reading. And then I read all the way to the end.

Here’s the thing. I don’t like WWII books (usually—I read Codename Verity earlier this year and it was fantastic, so maybe I’m on a roll here). I don’t like memoirs. And you know what? I still don’t understand how the codes worked, and I don’t intend to try to figure it out. But I had such a good time.

And that’s because Marks is a really good storyteller and a fantastic writer. He’s irreverent, snarky (as noted above), sarcastic (ditto), and self-deprecating. No one escaped his wit, particularly himself, and it is so much fun to read (until people started to die. That was really sad and put a damper on things.). I still don’t like WWII books, but Marks brings both a new perspective (cryptography) and a new style (cheeky memoir) to an often depressing and graphical violent genre. Definitely five stars.
160 reviews
January 5, 2014
Like listening to an old man tell stories from his time at war, this is a rambling memoir of vague accounts of incidental intelligence encounters. There is no chronology, no plot, no cohesive story, no greater authorial goals: in short, there is absolutely nothing for the reader to follow. To that end, the author even fails to describe the coding puzzles or how he solved them, merely smugly noting that he did. Between Silk and Cyanide was such an insufferable read by page 100 that I could not bring myself to go on.
Profile Image for David Crosby.
90 reviews4 followers
March 24, 2008
Good grief, what an excellent read. I'd settled down for what I assumed would be a dry but interesting read. Not at all, it was all about the characters, brought to life in a superb way. I was enthralled from start to finish, and only realised at the end that I had also been learning code breaking. Wow, will read again.
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