It is April 1900, in the Levant, on the imaginary island of Mingheria --- the 29th state of the Ottoman Empire --- located in the eastern Mediterranean between Crete and Cyprus. Half the population is Muslim, the other half are Orthodox Greeks, and tension is high between the two. When a plague arrives --- brought either by Muslim pilgrims returning from the Mecca or by merchant vessels coming from Alexandria --- the island revolts. To stop the epidemic, the Ottoman sultan Abdul Hamid II sends his most accomplished quarantine expert to the island --- an Orthodox Christian. Some of the Muslims, including followers of a popular religious sect and its leader Sheikh Hamdullah, refuse to take precautions or respect the quarantine. And then a murder occurs.

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.