Two of you exist. Only one will survive.

The city of Kersh is a safe haven, but the price of safety is high. Everyone has a genetic Alternate—a twin raised by another family—and citizens must prove their worth by eliminating their Alts before their twentieth birthday. Survival means advanced schooling, a good job, marriage—life.

Fifteen-year-old West Grayer has trained as a fighter, preparing for the day when her assignment arrives and she will have one month to hunt down and kill her Alt. But then a tragic misstep shakes West’s confidence. Stricken with grief and guilt, she’s no longer certain that she’s the best version of herself, the version worthy of a future. If she is to have any chance of winning, she must stop running not only from her Alt, but also from love . . . though both have the power to destroy her.

Cassia has always trusted the Society to make the right choices for her: what to read, what to watch, what to believe. So when Xander's face appears on-screen at her Matching ceremony, Cassia knows with complete certainty that he is her ideal mate . . . until she sees Ky Markham's face flash for an instant before the screen fades to black.

The Society tells her it's a glitch, a rare malfunction, and that she should focus on the happy life she's destined to lead with Xander. But Cassia can't stop thinking about Ky, and as they slowly fall in love, Cassia begins to doubt the Society's infallibility and is faced with an impossible choice: between Xander and Ky, between the only life she's known and a path that no one else has dared to follow.