The film shows Alan Turing and his team of code-breakers racing against time as they attempt to break Nazi Germany's Enigma code at Britain's top-secret Government Code and Cypher School at Bletchley Park during the Second World War. The group of scholars, mathematicians, linguists, chess champions and intelligence officers have a powerful ally in Prime Minister Winston Churchill who authorises the provision of any resource they require.
The film spans the key periods of Turing's life: his unhappy teenage years at boarding school; the triumph of his secret wartime work on the revolutionary electro-mechanical bombe, which was capable of breaking 3,000 Enigma-generated naval codes a day; and the tragedy of his post-war decline following his conviction for gross indecency, a criminal offence stemming from his admission of maintaining a homosexual relationship