Theo Lawder and Zac Bonneval meet in the army at the outbreak of World War II. They survive the horror of Dunkirk and become lovers. Theo goes to work at Bletchley Park, where he becomes friendly with Alan Turing. After the war he joins the Foreign Office, while Zac works for MI6. They make a good life together.
But this is a time when homosexuals are criminalised, and the pressure of being outcasts in society takes a terrible toll. Zac becomes deeply depressed and goes away. Can their love survive society's hatred?