It's July 1940, and eleven-year-old Lydia has just run away from life as a child evacuee in Wales. She arrives in her English village, gas mask in tow, only to find it abandoned. Her family's house is shuttered and empty, the windows covered by black-out blinds--but Lydia settles in, determined to wait there until they return. Late that night he comes: a wounded soldier, gun in hand, heralding a full-blown German invasion. There are, the man explains, certain rules that Lydia must now follow. He says he won't hurt Lydia, but she cannot leave the house. As the unlikely pair coexists in the claustrophobic confines of the house, each becomes dependent on the other for survival. But when Lydia tries to uncover what brought the soldier to her door, she realizes that he knows more than he should about her family--and that he's plotting something for them both.