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.