THE COLDITZ CIPHER

September 1943. The microfilm in his boot heel is worth more than his life, and its value expires in ninety days.

Colditz Castle is where the Reich sends the prisoners no other camp can hold. Flight Lieutenant Daniel Ash arrives with a secret that would get him shot in a courtyard rather than returned to a cell: before the war made him a bomber pilot, Bletchley made him a codebreaker.

On his first night, a dying stranger in the next cell passes a canister through a gap in the stone. Inside: film that must reach London before its window closes, carried by a courier who didn't live to explain who sent it, or why it bears a marking Ash has never seen.

Between Ash and the Swedish consulate at Leipzig stand four-storey walls, a winter cliff face, and an escape committee that trusts no new arrival. Watching them all is Oberleutnant Kellner, a quiet German intelligence officer with a taste for old cryptography journals, who is one footnote away from working out exactly who his newest prisoner used to be.

Ash has a Polish officer who maps stone by eye, a hollow boot heel, and a schedule written by the cipher itself. Every day inside the wire is a day off the film's value. And someone inside Colditz is already talking to the Germans.

A meticulously plotted novel of codebreaking, captivity, and escape, for readers of Robert Harris, Ben Macintyre, and Kate Quinn.