Dr. Sloane Mercer operates with cold precision, numbed by the unsolved murder of her brother. She fixes broken bodies and asks no questions. But when she saves the life of Luca Serrat—a lethal "problem solver" for the Calderay syndicate with two bullets in his chest—she unwittingly binds him to her.

Luca's twisted sense of debt manifests in silent surveillance and the delivery of handcrafted knives at her door, each blade inscribed with the name of a threat he has eliminated for her. He is a man who was built to take lives; she is a woman trained to save them. As danger closes in and the truth about her brother's death comes to light, their clinical detachment shatters. Forced into a safe house, they are pulled into a dark, sensual, and highly tactical game of survival where the lines between protector, predator, and patient disappear.

Some debts are paid in blood. Others in obsession.