Thirty-six murders solved out of thirty-seven. That of the chief inspector Alessandro Rossini and his partner Luca Bernardi is the highest percentage of case resolution of the entire Milan's Homicide Squad. A fact that everyone would be proud of, but for Rossini it is not so. That one unresolved case constantly populates his nightmares and has turned into an obsession that risks making him lose his wife.

When, finally, he seems to have managed to overcome the past, Rossini receives an unexpected phone call. A call that takes him back three years, at the time of the most difficult investigation in his career. In an instant, a dark and threatening past made of twelve victims without a culprit returns to haunt him.

And while the number of victims continues to rise, Rossini and Bernardi know that this time they can no longer fail.