Superintendent Teresa Battaglia, a trailblazing criminal detective on the Italian police force, is on sick leave, recovering from her recent brush with death in pursuit of a killer. But none of her colleagues, not even her partner, know that her Alzheimer’s is getting worse, and that she is unsure she will ever return to work. Teresa’s plans for retirement are shelved, however, when she is urgently summoned to meet with menacing serial killer Giacomo Mainardi. Refusing to speak with anyone but Teresa, whose investigative work 27 years prior landed him in maximum security prison, Mainardi has disconcerting news: somebody is after him, and only Teresa holds the key to keeping everyone, including herself, safe. To solve the case, Teresa must come face to face with a history she thought she’d buried.

A decades-old murder investigation has landed on Superintendent Teresa Battaglia's desk. DNA analysis has revealed that a painting from the final days of World War II contains matter from a human heart. Teresa is able to trace the evidence to Val Resia, one of Italy’s most isolated, untouched regions. When Teresa’s investigation hits too close to the truth, a fresh human heart is hung at the valley’s entrance, a warning not to cross its threshold. As she hunts a ruthless killer, Teresa must face down her own rapidly deteriorating physical and cognitive abilities, as well as someone she hoped never to see again --- a man who has just become her supervisor.

Superintendent Teresa Battaglia has fought for nearly four decades to earn rank and respect on a testosterone-heavy Italian police force. When she’s called to investigate a gruesome murder near a mountainside town, she’s paired with a young male inspector she’s not sure she trusts. But she has no choice. In this remote town full of secrets, eerie folktales and primal instincts, the killer seems drawn to a group of local children, who may be in grave danger. As Teresa inches closer to the truth, she must confront the possibility that her faculties, no longer what they once were, may fail her before the chase is over.