Charlotte finds it difficult to sleep her first night at boarding school, but she does manage to drift off in the uncomfortable bed. Waking in the middle of the night, she sees a cedar tree looming outside her window, outlined by a silver moon. The tree had not been there the night before. A trick of the light, Charlotte thinks, and she falls asleep again. But in the morning it's not just the tree that's new; the whole room is different, old-fashioned, and her roommate Susannah is gone, replaced by a strange girl named Emily, who insists on calling Charlotte "Clare." Is Charlotte dreaming, or could she have slipped back in time?