Investigating an arson attack, Alessandro and Irene meet a colleague from the explosives department who suspects a young but repeat offender. Simonelli takes it personally because he saw his best friend die during a fire set years earlier by the same deranged man. But Irene realizes that things are less straightforward than they seem, while Roberto manages to arrest the perpetrator of the car bomb commissioned by Patriarca. During a graduation party, a young and beautiful university professor is drugged and raped. But when she wakes up, Viviana doesn't remember anything and Luca and Anna will have to find out who took advantage of her. Meanwhile, Roberto, who has discovered Patriarca's home and hidden documents inside that concern a nursery, gets back on the trail of Cesare Carrano.