A university math professor, Emanuele Sarti, is found dead in a tunnel inhabited by a homeless man in Valentino Park. Strange mathematical formulas are discovered written on the walls of the tunnel: improbable that it's a coincidence.

After deciding to remain in Turin, Valeria returns to the crime scene of her father's murder and discovers a piece of evidence that has been overlooked in the past: that night, in the house on the lake, in addition to her mother and father, a third person has been present.

The entire Rocchi family is found dead in a hillside villa and all evidence points to a terrible case of homicide-suicide engineered by Sandro, the head of the family. But the youngest, Samuele, only six years old, is found alive and well in the trunk of the car. What if the whole thing was staged?