She is assigned to a wireless listening station, transcribing Enigma coded Morse transmissions from Nazi Germany and makes friends with Mary.

After an altercation in a pub she is moved to Bletchley Park, the centre of the code-breaking operation, only to find herself cleaning and making tea.

She overhears the male staff discussing the eponymous imitation game (as devised by Bletchley Park's Alan Turing).

Later Cathy is caught in Turner's room reading documents relating to the Ultra programme, and she is incarcerated in military prison for the remainder of the war.

[1] Writing in 1980, Ian McEwan stated: "Initially I wanted to write a play about Alan Turing, one of the founding fathers of modern computers', but his researches provided very little material, 'by this time other facts about Bletchley Park interested me more.