It's 1954. Several English nationals have defected to the USSR, while a witch hunt for homosexuals rages across Britain. In these circumstances, no one is surprised when a mathematician by the name of Alan Turing is found dead in his home: it is widely assumed that he committed suicide, unable to cope with the humiliation of a criminal conviction for homosexuality. But young Detective Sergeant Leonard Corell, who had always dreamt of a career in higher mathematics, suspects greater forces are involved. In the face of opposition from his superiors, he begins to assemble the pieces of a puzzle that lead him to one of the most closely guarded secrets of the war : the Bletchley Park operation to crack the Nazis' Enigma code. But he is also about to be rocked by two startling developments in his own life, one of which will find him being pursued as a threat to national security.