In the war-torn London of 1939, fourteen-year-old Hazel and five-year-old Flora are evacuated to a rural village to escape the horrors of the Second World War. But the unthinkable happens when young Flora suddenly vanishes while playing near the banks of the river. Shattered, Hazel blames herself for her sister's disappearance, and she carries that guilt into adulthood as a private burden she feels she deserves.