In the autumn of 2006, a woman named Clara moved into the top-floor apartment of a sprawling Victorian house in the small, tired town of Ravenswood, Pennsylvania. The rent was absurdly cheap, and she told herself that was because the place was dusty and old. But within a week, she noticed something wrong with the window in her attic—the one that faced the back of the house, sealed shut by paint and age. It wasn't the window itself that bothered her. It was the fact that every night, around eleven o'clock, a light would flicker on behind the frosted glass, even though there was no lightbulb in the room. Clara tried to ignore it. She tried to cover the window with a curtain. But the light kept returning, and soon she began to hear someone breathing on the other side. Luna tells Clara's story—the story of a woman who learned that some houses are not empty, and some doors are better left unopened.