Youngster Stefano Bianchi is killed in an illegal motorbike race. His bike was sabotaged, and he drugged. His fiancée Fabiola admits the dope in their apartment was supplied to both of them by dealer Germano 'the rat' Luccheri, who says there is big betting on the street races. Lorenzo's team also examines Stefano's employer, Ernesto Di Clemente's garage. Morini poses as a new racer. Rex apparently suffers from depression.