When brilliant math professor Ivy Reeves receives a cryptic note bearing her name at a crime scene, she's drawn into a deadly game where probability becomes a matter of life and death.

Thirteen victims. Complex mathematical puzzles. A killer who understands that some games are designed to be lost.

As Detective Vaughn Ryan races against the clock, he needs Ivy's genius to decode the twisted logic behind each murder. But the closer they get to the truth, the more personal the game becomes. The killer knows Ivy's past--the fire that destroyed her family, the secrets she's buried, the father she visits wearing a mask over his melted skin.

Every number has meaning. Every equation points to the next victim. And time is running out.

From New York Times bestselling author J.D. Barker and Patrick Logan comes a pulse-pounding thriller where mathematics meets murder, and one wrong answer means death.