Joan’s voice is almost a whisper. ‘Nobody talked about what they did during the war. We all knew we weren’t allowed to.’

Joan Stanley has a secret.

She is a loving mother, a doting grandmother, and leads a quiet, unremarkable life in the suburbs. Then one morning there is a knock on the door, and suddenly the past she has been so keen to hide for the last fifty years threatens to overturn her comfortable world.

Cambridge University in 1937 is awash with ideas and idealists, yet unworldly Joan feels better suited to a science lecture and a cup of cocoa. But a chance meeting with the glamorous Russian-born Sonya and her charismatic cousin Leo blurs the edges of the things Joan thought she knew about the world, and about herself.

In the post-War world of smoke and mirrors, allegiance is a slippery thing. Working in a government ministry with access to top-secret information, Joan is suddenly faced with the most difficult question of all: what price would you pay to remain true to what you believe? Would you betray your country, your family, even the man you love?