A serial killer on death row challenges a forensic linguist to solve his final puzzle in a novel of breathtaking mind games by the Wall Street Journal bestselling author of The Lies You Wrote.

Forensic psychologist Callum Kilkenny lost his wife, Shay, to the very serial killer he'd hunted for five years. When Nathaniel Conrad--known as the Alphabet Man, for his love of tattooing codes onto his victims' bodies--was condemned to death row, Callum thought the game of cat and mouse was over. But just before execution, Nathaniel drops a bombshell: he's not the one who murdered Shay.

After analyzing the killer's taunting, coded letters to authorities--one for each victim--FBI forensic linguist Raisa Susanto believes him. The discrepancies bear it out. So was it a copycat? A partner in crime? Or something more sinister? If Nathaniel knows the answer, Raisa fears he'll be taking that closely guarded secret to his grave.

As Raisa and Callum are pulled into an investigation to solve Shay's murder, it reopens old traumas that cut deeper than they could imagine. Before someone else dies, Raisa must decipher the unbelievable truth in an ever-twisting case built on a foundation of lies.