It follows the story of English born Joan Stanley, a Soviet and communist party sympathizer, who becomes employed as a British government civil servant. She later gets recruited by the KGB in the mid 1930s. She successfully transfers nuclear bomb secrets to the Soviet Union, which enables them to keep up with the west in the development of atomic weapons, and remains undetected as a spy for over a half a century. Directed by Trevor Nunn, the film is based on Melita Norwood's life, a British spy who spent most time in the service of the KGB. Judi Dench ('Skyfall') leads a cast composed by Tom Hughes ('Realive'), Sophie Cookson ('Kingsman: The Golden Circle') and Tereza Srbova ('Eastern Promises')