Tom Shaw decides to give it a miss - until his flatmate Alistair unexpectedly enlists, and the conflict can no longer be avoided.
Young, bright and brave, Mary is certain she'd be a marvelous spy. When she is - bewilderingly - made a teacher, she instead finds herself defying prejudice to protect the children her country would rather forget.
Tom, meanwhile, finds that he will do anything for Mary.
And when Mary and Alistair meet, it is love, as well as war, that will test them in ways they could not have imagined, entangling three lives in violence and passion, friendship and deception, inexorably shaping their hopes and dreams.
In a powerful combination of both humour and heartbreak, this dazzling novel weaves little-known history, and a perfect love story, through the vast sweep of the Second World War - daring us to understand that, against the great theatre of world events, it is the intimate losses, the small battles, the daily human triumphs, that change us most.