'The Sleeping Nymph': a work of art of magnetic beauty, painted by a young partisan fighter during the last days of the Second World War. A painting carrying a shocking secret hidden in the red pigment on the canvas, made with the blood of a human heart.

But whose heart?

There is no body, no confession. Only that faint trace of blood. And that's what leads commissioner Teresa Battaglia - herself hiding an unspeakable truth - to the Resia Valley, in the north eastern part of Italy: a perfect genetic enclave protected for centuries from the outside world.

The valley and the portrait are the only clues for a murder that occurred more than 70 years before. A red thread leading to the shadow of someone hell-bent on protecting a sacred secret.