Stolen from his family by changelings, Henry Day is given the name "Aniday" by the ageless and magical beings, who replace him with another child who takes his place with his parents, a young boy who possesses an extraordinary gift of music.

Sixteen-year-old Mackie Doyle knows that he replaced a human child when he was just an infant, and when a friend's sister disappears he goes against his family's and town's deliberate denial of the problem to confront the beings that dwell under the town, tampering with human lives.

Everyone says Lauren Tranter is exhausted, that she needs rest. And they're right; with newborn twins, Morgan and Riley, she's never been more tired in her life. But she knows what she saw: that night, in her hospital room, a woman tried to take her babies and replace them with her own...creatures. Yet when the police arrived, they saw no one. Everyone, from her doctor to her husband, thinks she's imagining things. A month passes. And one bright summer...