Bruno Testori is the director of the San Michele prison where he uses unorthodox methods towards the prisoners. One morning the body of Nicola Iaccarino, commander of the penitentiary police and best friend of Bruno, is found, who does not want to spread the news and begins internal personal investigations that will lead to nothing. Testori then turns to the deputy prosecutor Lombardo who investigates alongside Inspector Pellegrini discovering that the commander was attacked on the roof and thrown downstairs. Testori seeks the help of Miroslav Lackovic, a former drug trafficker serving a life sentence, to try to understand what really happened but he is found hanged in his cell.

Testori forces a North African prisoner to become his spy by infiltrating the Muslim group in exchange for a favorable report that the director would write. The director has bugged the cells so that he can listen to all the conversations including the one between Lombardo and Ciocci, an inmate with serious drug problems who is promptly transferred to prevent him from collaborating with her. The first clashes between Slavs and Nigerians begin and Massini to restore order agrees with Goran, who in fact becomes the successor of Lackovic, and Mansur. Testori instead makes an agreement with Aniello. Lombardo discovers that Testori had returned to prison in the middle of the night on the night of Lackovic's death and asks his superior to investigate further on the director.