From a distance, the Haven Institute, tucked away on a private island off the coast of Florida, looks serene and even beautiful. But up close the locked doors, military guards, and biohazard suits tell a different story. In truth, it is a clandestine research facility where thousands of replicas, or human models, are born, raised, and observed.

But when a surprise attack is launched on Haven, two of its young experimental subjects—Lyra, or 24, and the boy known only as 72—manage to escape. As they make their way through a new and menacing environment, they meet a stranger named Gemma, who has embarked on a perilous quest of her own. And as Lyra tries to understand Haven’s purpose, she uncovers earth-shattering secrets that will change the lives of both girls.

Gemma has been in and out of hospitals her whole life. A sickly child, she has grown into a lonely adolescent whose life is circumscribed by home, school, and her best friend, April.

But after she is nearly abducted by a stranger claiming to know her, Gemma starts to investigate her family’s past and discovers her father’s mysterious connection to the secretive Haven research facility. Hungry for answers, she travels to Florida, only to stumble upon two human models, or replicas, 24 and 72—and a completely new set of questions. As Gemma tries to unravel the mysteries of Haven, she learns terrible truths about herself and her family that will threaten to destroy everything she loves.

While the stories of Gemma and Lyra mirror each other, each contains breathtaking revelations critically important to the other story. Their narratives can be read separately or in alternating chapters. In either case, the two distinct parts of this astonishing novel combine to produce an unforgettable experience for its two young heroines—and for the reader.