Giselle Jakobs' grandfather was the last person executed at the Tower of London. A family man who ran afoul of the Nazis, Josef Jakobs was ill-prepared for an espionage mission to England. Captured by the Home Guard after breaking his ankle, Josef was interrogated at Camp 020. Rejected as a double-agent, he was then prosecuted under the Treachery Act and executed by firing squad on 15 August 1941. It would seem to be an open and shut case, yet Josef’s MI5 file suggests otherwise. Faced with the threat of a German invasion in 1940-41, MI5 used promises and threats to break enemy agents, extract valuable intelligence and occasionally turn them into double agents. Evidence in his file suggests that the German Intelligence Service set Josef up to fail; sacrificed as a 'canary in the coal mine' to test MI5’s double-cross system. The Spy in the Tower tells the untold story of one of Nazi Germany’s failed agents. It calls into question the legality of Britain’s wartime espionage trials and the success of its double-cross system.