The Shadow Code

by Suzy Henderson

When a WPC cracks a cipher, she ignites a fuse that could bring down a nation.

London, autumn 1940. As the Blitz ravages the city, WPC Ellie Harcourt is called to the scene of a murdered civil servant. Sewn into his coat is a cryptic cipher referencing 'Kingfisher', a codename whispered in intelligence circles. Still reeling from the disappearance of her lover, Sinclair, Ellie suspects the cipher points to something far deeper than a conspiracy inside Whitehall.

When MI5 takes over the case, Ellie is paired with officer Jack Stratton – an old acquaintance from society circles with a long memory and a grudge. Their reluctant partnership intensifies when another agent is found dead, another cipher appears, and Ellie’s father – a scientist working on Britain’s top-secret radar programme – vanishes without explanation.

Ellie’s investigative skill and her ability to partially crack the cipher catch MI5’s attention, and she’s invited to consult on the case. As she and Jack grow closer and start to piece together the Kingfisher network, they realise the conspiracy reaches the very heart of Churchill’s inner circle. With traitors hidden in plain sight and time running out, Ellie must risk everything to stop a betrayal that could cost Britain the war.

Genres: Historical Fiction

363 pages, Kindle Edition

Published August 28, 2025

About the author

Suzy Henderson writes historical fiction, historical fantasy, and contemporary romance.

Her novel Madame Fiocca—based on the incredible true story of Nancy Wake, one of the most decorated women of WWII—has captivated readers worldwide.

Her debut novel, The Beauty Shop, was awarded the B.R.A.G. Medallion and explores the remarkable work of Sir Archibald McIndoe and the RAF airmen of the Guinea Pig Club.

Suzy studied creative writing and English Literature at The Open University and fell in love with storytelling. Now, she brings the past to life through her fiction, often weaving together history, resilience, and untold heroism. She lives on the edge of the Lake District, a place that continually inspires her writing.

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Reviews

[Lisa · Rating 5 out of 5]

The Shadow Code grabbed me from the first page and didn't let go until I reluctantly reached the end. Set during the beginning of the Blitz, the story encompasses the reluctance to allow women to take on roles previously held exclusively by men, as well as the fact that there were men in the government who supported Hitler. To that end, they were willing to give Britain's most sensitive war secrets to the Nazis. I loved the main character, Ellie Harcourt. She's brilliant, an Oxford math whiz, and horrifies her mother by working at Scotland Yard instead of marrying someone of her social class. The Shadow Code is a twisty spy story with a touch of romance, and well-known historical figures and events are cleverly written into the plot. I loved it.

[B · Rating 5 out of 5]

A Gripping Thriller of Secrets & Spies: I really enjoyed this book and was hooked from the first page. The Blitz setting felt so real, brought to life in incredible detail. Ellie is a great character. She’s clever and determined but still very human, and her partnership with Jack crackles with tension. The story moves at a good pace, with plenty of twists and a bit of heart too. The mix of real history (like the radar programme and the Tizard Mission) and espionage kept me gripped. If you enjoy historical mysteries with heart and atmosphere, this is a must-read.

[Sandy McKenna · Rating 5 out of 5]

A cleverly woven story.

WPC Ellie Harcourt is excellent at deciphering codes, so following the murder of a civil servant, she is transferred to MI5. Ellie is partnered with an old acquaintance, and has to prove that she is worthy of his trust.
An extremely cleverly woven story with plenty of twists and turns, well written and researched, and one which I could easily recommend.