In the FBI’s Naturals program, Cassie Hobbes has found a family and a purpose—but she’s never lost sight of her original goal to uncover the truth about her mother’s murder. Now she’s reeling from a stunning discovery: Lorelai Hobbes is alive, and held captive by a powerful and twisted cult of serial killers who call themselves the Masters. Their bloody legacy stretches back generations, and Cassie fears that they will have twisted her beloved mother into something else entirely.

Worse, the Masters have started killing again. With every body found, Cassie and her friends get closer to the truth at the bottom of the sadistic rabbit hole. But it soon becomes clear that the Masters’ reach goes farther and deeper than the Naturals could have imagined, and that even as they close in on Cassie’s mother, they may be playing right into the Masters’ hands.