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, Inspector Marini - know that her Alzheimer's is getting worse, and that Teresa is unsure she will ever return to work. Teresa's plans for retirement are shelved, however, when she is urgently summoned to meet with serial killer Giacomo Mainardi. Refusing to speak with anyone but Teresa, whose investigative work twenty-seven 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 past she thought she'd buried, back to when Giacomo first began to kill, and Teresa - newly pregnant and married to an abusive man - did everything she could to catch him.