Coliandro has to protect Giacomino, a peculiar, funny and ingenious character who has seen something he shouldn't have seen and who is threatened with death.

Coliandro believes that Gamberini has relapsed into the old habit of gambling and, trying to help his friend, infiltrates a clandestine gambling ring. In doing so, however, he blows up an investigation already underway promoted by Longhi and puts Giacomino, who he has hired as a consultant, Gamberini and himself in grave danger. Thanks to the help of Ambra, the girlfriend of one of the criminals, the inspector still manages to get away.

Coliandro seems to be on the verge of positively concluding a gallant adventure. But, at the climax, Giacomino shows up at his house, sleepy, hungry and with handcuffs on his wrists. The motivation is incredible: Giacomino is accused of being the author of a series of brutal murders. To help his friend, Coliandro will have to hunt down the real serial killer.