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The Imitation Game

In 1951, mathematician Alan Turing is questioned by police after an apparent home break-in, and he obliquely refers to his work at Bletchley Park during World War II.

In 1928, Turing, constantly bullied at boarding school, befriends Christopher Morcom, who sparks his interest in cryptography. Turing develops romantic feelings, but Christopher dies of bovine tuberculosis before he can confess.

When Britain declares war on Germany in 1939, Turing is an established mathematician. He joins the cryptography team of Hugh Alexander, John Cairncross, Peter Hilton, Keith Furman, and Charles Richards in Bletchley Park, directed by Commander Alastair Denniston. Their main employment is analysis of the Enigma machine the Wehrmacht uses to send coded messages. Difficult to work with, and believing his colleagues to be inferior, Turing works alone to design a deciphering machine, which he names "Christopher". When Denniston refuses to fund the £100,000 construction cost, Turing contacts Prime Minister Winston Churchill who appoints him as team leader and provides the funds. Turing then fires Furman and Richards and places a difficult crossword in newspapers as a test to find replacements.

Cambridge graduate Joan Clarke passes Turing's test but her family refuses her permission to work with the male cryptographers. Turing arranges for her to live and work with the women who intercept the messages, and shares his plans with her. Clarke helps Turing warm to the others, who begin to respect him. Turing's machine is constructed but cannot determine the Enigma encryption settings quickly enough, as the Germans reset them each day. Denniston orders it destroyed and Turing fired, and the other cryptographers threaten to leave. When Clarke plans to quit because of her parents, Turing proposes, which she accepts. During their engagement party, Turing confirms his homosexuality to Cairncross, who advises him to keep it a secret.

Overhearing a clerk talking about messages received from the same German coder, Turing has an epiphany: he can program the machine to decode words he knows exist in certain messages. The theory is proven correct when the German coder consistently opens messages with a standard plaintext German script, which reveals enough of the daily Enigma code to permit decoding of that day's messages. The cryptographers celebrate this breakthrough. Discovering through decoded intercepts that a convoy is in danger of a German attack, Turing fears a sudden response will notify the Germans that Enigma is compromised and change it. The team concludes they cannot act on every decoded message, and they issue no warning about the attack on the convoy, even though Peter, whose brother is serving in the convoy, begs them. Turing creates a statistical model to select which intelligence to act on, to maximize effect on the enemy while minimizing the risk of German suspicion.

Turing confronts Cairncross, who he has uncovered as a Soviet spy. Cairncross argues the Soviets are allies working for the same goals, and threatens to retaliate by disclosing Turing's sexuality. When MI6 agent Stewart Menzies appears to threaten Clarke, Turing shares his revelation about Cairncross. Menzies reveals in turn that he already knew, and is using Cairncross to leak misinformation to the Soviets for British benefit. Turing urges Clarke to leave Bletchley Park and admits his sexuality. She admits always being suspicious but insists they would have been happy together anyway. Fearing for her safety, Turing replies he never cared for her, and only used her for her cryptography skills. The heartbroken Clarke stays on, defying her parents and Turing.

After the war, Menzies has the cryptographers destroy all traces of the project, as MI6 wants foreign governments to feel secure using their own code machines without fear of British interception. The team is instructed never to meet again or share what they have done. In 1952, Turing is convicted of gross indecency and undergoes chemical castration to be spared from prison so he can continue his work. Clarke visits him, witnesses his physical and mental deterioration, and tries to comfort him.

The epilogue shows Turing committed suicide on June 7, 1954, after a year of government-mandated hormonal therapy. In 2013, Queen Elizabeth II granted him a posthumous Royal Pardon. Historians estimate that breaking Enigma shortened the war by over 2 years, saving over 14 million lives. Turing's work is now recognized as an essential step toward the development of modern computers.