On the night that she was killed, Irene played her final concert. First violin in an orchestra and the daughter of Adele Rubini, the owner of a prestigious theatre, she was a talented and beautiful young woman.

This time, however, Valeria isn't there to question those close to the victim as she is in Rome regarding her imminent transfer. Andrea Russo, her right hand man, sees to it, not as talented but definitely just as interesting. To convince Valeria to stay Lombardi promises that they will reopen the case of her father's murder.

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.