What do you think?
Rate this book
Master Mercurius Mysteries #9
Nun Shall Sleep
Another complex case falls in the lap of Master Mercurius! Perfect for fans of Andrew Taylor, C J Sansom, S J Parris and Ken Follett.
Mercurius can’t believe his luck … but are things too good to be true?
1689
Master Mercurius is making plans for a holiday tour of cathedrals when a letter arrives from Abbess Mathilde asking for his help.
Her convent has been left a substantial legacy which the abbess plans to use to fill the library, and she would like Mercurius to be in charge of buying the books.
Mercurius has never accepted a mission so quickly.
But as the summer wears on, strange things start to happen in the convent. A precious relic goes missing and an important key is lost.
Mercurius is fairly certain somebody is up to something, but he doesn’t know who and he doesn’t know what.
Desperate to hold on to the dream position he has been given, he finds himself drawn into the mystery.
But is there something more sinister going on…?
Nun Shall Sleep is the ninth historical murder investigation in the Master Mercurius Mystery atmospheric crime thrillers set in seventeenth-century Europe.
Mercurius can’t believe his luck … but are things too good to be true?
1689
Master Mercurius is making plans for a holiday tour of cathedrals when a letter arrives from Abbess Mathilde asking for his help.
Her convent has been left a substantial legacy which the abbess plans to use to fill the library, and she would like Mercurius to be in charge of buying the books.
Mercurius has never accepted a mission so quickly.
But as the summer wears on, strange things start to happen in the convent. A precious relic goes missing and an important key is lost.
Mercurius is fairly certain somebody is up to something, but he doesn’t know who and he doesn’t know what.
Desperate to hold on to the dream position he has been given, he finds himself drawn into the mystery.
But is there something more sinister going on…?
Nun Shall Sleep is the ninth historical murder investigation in the Master Mercurius Mystery atmospheric crime thrillers set in seventeenth-century Europe.
156 pages, Kindle Edition
First published January 9, 2026
104 people are currently reading
36 people want to read
About the author
Graham Brack
28 books153 followersGraham Brack trained as a pharmacist but now writes crime fiction. He has been shortlisted three times for the Crime Writers Association's Debut Dagger (2011, 2014 and 2016) without ever winning it. Those three entries involved three different detectives.
The 2011 entry has been published as Lying and Dying by Sapere Books, and has been followed by seven more books about Josef Slonský, a Prague policeman, and his team.
The 2014 offering has been published as Death in Delft and features Master Mercurius, a seventeenth century university lecturer. The second Mercurius mystery, Untrue till Death followed in August 2020 and the third in the series Dishonour and Obey in October 2020. The fourth, The Noose's Shadow arrived in December 2020 and The Vanishing Children in 2021. The sixth book was The Lying Dutchman (2022) and the seventh was Murder in Maastricht (2023). The latest is The Moers Murders . The ninth in the series, Nun Shall Sleep, will be published in January 2026.
Graham is married to Gillian and has two adult children and three granddaughters. He lives in a small village in Northamptonshire.
The 2011 entry has been published as Lying and Dying by Sapere Books, and has been followed by seven more books about Josef Slonský, a Prague policeman, and his team.
The 2014 offering has been published as Death in Delft and features Master Mercurius, a seventeenth century university lecturer. The second Mercurius mystery, Untrue till Death followed in August 2020 and the third in the series Dishonour and Obey in October 2020. The fourth, The Noose's Shadow arrived in December 2020 and The Vanishing Children in 2021. The sixth book was The Lying Dutchman (2022) and the seventh was Murder in Maastricht (2023). The latest is The Moers Murders . The ninth in the series, Nun Shall Sleep, will be published in January 2026.
Graham is married to Gillian and has two adult children and three granddaughters. He lives in a small village in Northamptonshire.
Ratings & Reviews
Friends & Following
Create a free account to discover what your friends think of this book!
Community Reviews
Displaying 1 - 21 of 21 reviews
January 26, 2026
The year is 1689 and Master Mercurius is planning a holiday tour of cathedrals when he is invited to visit Abbess Mathilde and oversee the expansion of her Convent's library. What more could he ask for but there is a catch. He needs to travel there in charge of a young woman who wishes to become a nun. What follows are the usual disasters which always pursue Mercurius wherever he goes despite his constant belief that nothing is ever his fault.
I do so enjoy this series. Master Mercurius is the most entertaining character and his comments are frequently laugh aloud funny. I enjoyed the mystery at the Convent and felt very smart when I solved the crime before Mercurius did. I loved the way the book closed with a particular problem solving itself in his favour. In fact I found the whole book to be perfect and would give it more than five stars if I could! Looking forward to book ten.
I do so enjoy this series. Master Mercurius is the most entertaining character and his comments are frequently laugh aloud funny. I enjoyed the mystery at the Convent and felt very smart when I solved the crime before Mercurius did. I loved the way the book closed with a particular problem solving itself in his favour. In fact I found the whole book to be perfect and would give it more than five stars if I could! Looking forward to book ten.
January 12, 2026
Nun Shall Sleep is the ninth book in the Master Mercurius Mysteries series by British author, Graham Brack. Master Mercurius is not at all upset when his summer holiday plan for 1689, to visit some German cathedrals, is hijacked by a request from Mathilde. The much respected, and also gracious, elegant and beautiful Abbess asks if he will accompany a young woman from Pijnacker to their convent near Melle, where she will become a postulant nun. Her father is not well enough to withstand a return journey that will likely take up more than three weeks.
The sweetener is that the convent has received a munificent bequest for the purchase of books for their library, and Mathilde would like his advice on what to buy. Mathilde’s company, spending time in the convent library, reading books new to him, and buying books: sounds as close to Heaven as he could get on Earth.
Liese de Uyl seems resigned to the fact that there is no dowry for her, and appears genuine in her wish to serve God, but Mercurius does find her overly talkative, a bit shallow and somewhat spoiled. When they arrive at the convent, she takes readily to convent life. Mercurius is happily absorbed in cataloguing the library and anticipating what might be added to it. Adding to his joy is the fact that he can say mass for the nuns: Mathilde had earlier twigged to his secret ordination as a Catholic priest.
His stay involves a book buying trip to Hanover, with Mathilde and another of the sisters, driven in the convent’s carriage by handyman Thomas. They extend their trip to include Braunschweig and Magdeburg, and there’s a bit of excitement when their carriage is held up by armed would-be thieves on the return journey.
While he immerses himself in the glorious task of cataloguing the new purchases, a few little incidents distract. One of the relics in the convent’s treasury, the thong of St Pauls sandal, goes mysteriously missing, then just as mysteriously reappears. A key to the treasury strong box is lost, then found. And a badger trap catches something larger. Evidence of interference with the mortar in one of the walls has Mercurius wondering, as his departure date looms, whether the nuns are in any danger.
It's always a pleasure to read the latest exploits of Leiden University’s seventeenth Century philosophy lecturer, Master Mercurius. His deductive discussions with Thomas the handyman, and later, the constable, about the potential thieves, and the logistics and tactics they might employ to catch them, are engaging, while his many asides to his scribe, Van der Meer are always a source of humour.
Mercurius often has comments to make about the Dutch people and their behaviour. In this instalment, he compares the language to German, which “sounds a little like Dutch, though not, of course, so melodious” and is “just Dutch with the clever bits left out”. Of himself, Mercurius says “As will have been clear from these volumes, I am not an epicurean, and usually eat sparingly” which is quite a contrast with Brack’s other protagonist, Josef Slonský, whose prodigious appetite is well-known. Another delightfully entertaining dose of Master Mercurius.
The sweetener is that the convent has received a munificent bequest for the purchase of books for their library, and Mathilde would like his advice on what to buy. Mathilde’s company, spending time in the convent library, reading books new to him, and buying books: sounds as close to Heaven as he could get on Earth.
Liese de Uyl seems resigned to the fact that there is no dowry for her, and appears genuine in her wish to serve God, but Mercurius does find her overly talkative, a bit shallow and somewhat spoiled. When they arrive at the convent, she takes readily to convent life. Mercurius is happily absorbed in cataloguing the library and anticipating what might be added to it. Adding to his joy is the fact that he can say mass for the nuns: Mathilde had earlier twigged to his secret ordination as a Catholic priest.
His stay involves a book buying trip to Hanover, with Mathilde and another of the sisters, driven in the convent’s carriage by handyman Thomas. They extend their trip to include Braunschweig and Magdeburg, and there’s a bit of excitement when their carriage is held up by armed would-be thieves on the return journey.
While he immerses himself in the glorious task of cataloguing the new purchases, a few little incidents distract. One of the relics in the convent’s treasury, the thong of St Pauls sandal, goes mysteriously missing, then just as mysteriously reappears. A key to the treasury strong box is lost, then found. And a badger trap catches something larger. Evidence of interference with the mortar in one of the walls has Mercurius wondering, as his departure date looms, whether the nuns are in any danger.
It's always a pleasure to read the latest exploits of Leiden University’s seventeenth Century philosophy lecturer, Master Mercurius. His deductive discussions with Thomas the handyman, and later, the constable, about the potential thieves, and the logistics and tactics they might employ to catch them, are engaging, while his many asides to his scribe, Van der Meer are always a source of humour.
Mercurius often has comments to make about the Dutch people and their behaviour. In this instalment, he compares the language to German, which “sounds a little like Dutch, though not, of course, so melodious” and is “just Dutch with the clever bits left out”. Of himself, Mercurius says “As will have been clear from these volumes, I am not an epicurean, and usually eat sparingly” which is quite a contrast with Brack’s other protagonist, Josef Slonský, whose prodigious appetite is well-known. Another delightfully entertaining dose of Master Mercurius.
January 25, 2026
I stumbled upon this author many years ago now and boy am I glad I did. Graham Brack has two series going on, one about Josef Slónsky a police in Prague and this one about Master Mercurius, a monk in Leiden set in the late 1600s. I was not a big fan of this series at first but it has grown on me and now I love it. Mercurius dreams of an easy living with food, drink and books just like me but his life is definitely not like that. He stumbles on one mysterious happening after the other, sometimes even murder. Often he is called into service by the Stadhouder to solve problems wherever they may occur. Brack has a great feeling for the setting and time these books is set in and it's a pure joy reading. I will not say that Mercurius is the most clever fellow but he gets the job done. Sometimes by accident. In this book our "hero" is set to take a sort of vacation and visit some cathedrals but fate has something completely different in store for him. He is to escort a young girl to a convent and when he arrives there he is asked to go through there library and help them with buying new books. It's like a drem come true for any lover of books. While there things happen and maybe Mercurius will figure it out. I loved this story and the characters and the parts about books are great. I really recommend this author and series for fans of good books and historical fiction.
January 10, 2026
9 1/2 books to date featuring Master Mercurius, all of them greatly entertaining and one of my favorite series. I had to award the fifth star this time round as it was especially pleasing to be reading one of his adventures again seeing him welcomed into a convent to work on their library.
Kindle Unlimited
Kindle Unlimited
February 14, 2026
Delightful as usual,but not as brilliant as the previous ones.
January 16, 2026
It felt so good to be back reading the memories of the aged Master Mercurius as dictated to his long suffering scribe Van der Meer. I was surprised to see that this is the 9th volume. I suppose that like time, books pass more quickly when you're enjoying them.
With William now safely away on the throne of England, Mercurius is looking forward to a real vacation (visiting Cathedrals) when the long summer holidays arrive at the University of Leiden. His plans change and he jumps at the opportunity to act as chaperone for a local young lady who wishes to join the convent of his friend Abbess Mathilde, for he is invited to stay there for the summer to build and catalogue their library. A dream job for him.
During his stay certain things happen which raise his suspicions that something untoward is being planned.
There is so much about this series to like. There is a gentle humour in the old character himself shown in his exchanges with others but mainly with the 'aside' comments to his scribe. The way other writers seem to pad out boring journeys or meals is absent here and everything reads so well as part of the story. In this episode there are certainly no murders to solve and such death as there is, swiftly dealt with and bloodshed minmal and almost accidental. Added to this you have a, perhaps rose tinted, view of life in late 17th century Holland/ Northern Germany.
If cozy equals feel good then this is it.
As well as the story itself, I found the dedication more heartfelt than usual and the authors 'Notes to Readers' at the end both amusing and informative. I can vouch for the comment that he loves to hear from readers as I was surprised by the prompt and charming reply that I received from a message I sent to him recently.
I wonder what will be next, a new Mercurius or a new Slonsky or maybe a new character altogether. Can't wait.
15th Jan 2026
With William now safely away on the throne of England, Mercurius is looking forward to a real vacation (visiting Cathedrals) when the long summer holidays arrive at the University of Leiden. His plans change and he jumps at the opportunity to act as chaperone for a local young lady who wishes to join the convent of his friend Abbess Mathilde, for he is invited to stay there for the summer to build and catalogue their library. A dream job for him.
During his stay certain things happen which raise his suspicions that something untoward is being planned.
There is so much about this series to like. There is a gentle humour in the old character himself shown in his exchanges with others but mainly with the 'aside' comments to his scribe. The way other writers seem to pad out boring journeys or meals is absent here and everything reads so well as part of the story. In this episode there are certainly no murders to solve and such death as there is, swiftly dealt with and bloodshed minmal and almost accidental. Added to this you have a, perhaps rose tinted, view of life in late 17th century Holland/ Northern Germany.
If cozy equals feel good then this is it.
As well as the story itself, I found the dedication more heartfelt than usual and the authors 'Notes to Readers' at the end both amusing and informative. I can vouch for the comment that he loves to hear from readers as I was surprised by the prompt and charming reply that I received from a message I sent to him recently.
I wonder what will be next, a new Mercurius or a new Slonsky or maybe a new character altogether. Can't wait.
15th Jan 2026
January 17, 2026
Master Mercurius books are painstakingly researched with lovely historical details. The master himself is delightful, combining equal parts of intelligence, self-deprecation, and ego. and ego. I highly recommend the whole series.
January 15, 2026
Probably the least interesting Master Mercurius Mystery so far.
January 13, 2026
Rejoice—another Master Mercurius book!
This instalment is slightly different, as Mercurius is invited by Abbess Mathilde to her convent to assist with acquiring books for the library. It is a dream come true for him, but soon after his arrival, a series of strange incidents occur, calling upon his talents for unraveling mysterious events.
As always, the story is full of charm and wit, and the exchanges with his clerk, Van der Meer, are particularly amusing.
Another wonderful addition to the series.
This instalment is slightly different, as Mercurius is invited by Abbess Mathilde to her convent to assist with acquiring books for the library. It is a dream come true for him, but soon after his arrival, a series of strange incidents occur, calling upon his talents for unraveling mysterious events.
As always, the story is full of charm and wit, and the exchanges with his clerk, Van der Meer, are particularly amusing.
Another wonderful addition to the series.
January 12, 2026
Too short and superficial. At 154 pages, the witty banter and asides to his scribe are enjoyable, but they took up half of this book. The mystery was hardly one at all, and I had figured it out early on. The time spent on the sick prostitute took another 1/5 or the book that had nothing to do with the incredibly weak mystery. I do like the background and the descriptions of everyday life, but this was no mystery.
January 20, 2026
Entertaining
Master Mercurius is a lecturer at a Dutch Reformed university. He spends the summer in Germany at a Catholic nunery helping with acquisitions for their library. While there he discovers mischief .
I have read all nine of this series and enjoyed them very much.
Story is set in the 17th century shortly after William of Orange and Mary have taken the English throne.
Master Mercurius is a lecturer at a Dutch Reformed university. He spends the summer in Germany at a Catholic nunery helping with acquisitions for their library. While there he discovers mischief .
I have read all nine of this series and enjoyed them very much.
Story is set in the 17th century shortly after William of Orange and Mary have taken the English throne.
January 20, 2026
This had to be the slowest of the series. Yes, we get a summer with Master Mercurius buying books for a convent. It's theft, not murder and a very thin mystery as the culprit was pretty obvious from the start. Also Master M seemed to be rather dunderheaded throughout with the fun coming from his absurb conversations with Thomas and remarks to Van der Mir. Oh well, a bit of 17th century keystone cop isn't too bad.
Can't wait for the next one.
Can't wait for the next one.
February 14, 2026
Master Mercurius Almost Takes A Vacation
However when the Abbess calls and offers him the chance to buy books for her abbey, Mercurius jumps into action. Accompanying a young woman who plans to become a nun, their arrival sets in motion a chain of events that Mercurius must learn the meaning of.
I simply love crotchety, old Mercurius and his long suffering scribe. More stories, please!
However when the Abbess calls and offers him the chance to buy books for her abbey, Mercurius jumps into action. Accompanying a young woman who plans to become a nun, their arrival sets in motion a chain of events that Mercurius must learn the meaning of.
I simply love crotchety, old Mercurius and his long suffering scribe. More stories, please!
January 12, 2026
1689 Abbess Mathilde wants the help of Master Mercurius. The convent has been given a bequest which she wishes to spend on books and needs his help to do so. A dream come true for him. But on arrival strange happenings occur.
An entertaining and well-written historical mystery. Another good addition to this enjoyable series.
An entertaining and well-written historical mystery. Another good addition to this enjoyable series.
Read
January 22, 2026A lovely novel
I've read all the previous Mercurious books and this is of the same high standard. The book just flows along and it is so difficult not to just read one more chapter! Hope I dont have to wait too long for the next book!
I've read all the previous Mercurious books and this is of the same high standard. The book just flows along and it is so difficult not to just read one more chapter! Hope I dont have to wait too long for the next book!
January 25, 2026
An excellent ,at times amusing ,and entertaining read
Mercurius after a few missteps solves the case .
The story is set in a convent in Germany where he can fulfil his role as a Catholic priest giving services for the nuns .
Mercurius after a few missteps solves the case .
The story is set in a convent in Germany where he can fulfil his role as a Catholic priest giving services for the nuns .
February 13, 2026
Ingenious and insightful
Overall I liked the style of writing and the interplay of teller and imanuensis. Clever working out of the mystery and a good sharing of the history and connections of culture.
Overall I liked the style of writing and the interplay of teller and imanuensis. Clever working out of the mystery and a good sharing of the history and connections of culture.
February 17, 2026
Wonderful
Wonderful, subtle humor that can't be beat. Hope that there are many more volumes in this uniquely odd and wonderful character's interesting and strange life. How does the author come up with all these wild things?
Wonderful, subtle humor that can't be beat. Hope that there are many more volumes in this uniquely odd and wonderful character's interesting and strange life. How does the author come up with all these wild things?
January 19, 2026
Master storyteller
Another fine Master Mercuries tale. Intrigue spiced with humour and historical mystery.
I hope that we soon hear more from the busy pen of Graham Brack.
Another fine Master Mercuries tale. Intrigue spiced with humour and historical mystery.
I hope that we soon hear more from the busy pen of Graham Brack.
January 20, 2026
New stories are many and even some fun!
Master Mercurius was challenged throughout the story. A nice portrait of life in Germany and convent life in the 17th Century. Well done!
Master Mercurius was challenged throughout the story. A nice portrait of life in Germany and convent life in the 17th Century. Well done!
February 18, 2026
A nice story set in Germany with an intriguing plot.
Displaying 1 - 21 of 21 reviews