When Boston private investigator Patrick Kenzie meets Karen Nichols, she strikes him as an innocent from a protected upbringing. But six months later when Karen takes her own life, Patrick is left wondering what can change so drastically and so quickly that suicide seems the only option?

Through the final weeks of a stifling summer, and with the help of his ex-partner, Angela Gennaro, and his friend, the lethally unbalanced Bubba Rogowski, Patrick enters into psychological warfare with a brilliant sociopath who, instead of merely killing his victims, prefers to make them wish they were dead.

As the stakes grow higher and more personal, they find themselves fighting a losing battle with an enemy the law can't touch, who is always one step ahead, who is gradually discovering their weaknesses, their loves, and is determined to tear their world apart.