London 1939 and the city's children must be evacuated to the countryside to keep them safe from the German bombs. After a tearful goodbye at the station, Peggy Larkin is sent to live with strangers in the country, unsure if she'll ever see her parents again. Peggy meets the ultra strict Mrs Henderson and does her best to fit into country life. But what secret lies behind the locked door in the big house? Who is the man hiding out in the woods? Peggy finds a friend in Alfie, another London evacuee and together they try to solve the mystery.