Inspector Leonardo Tanzi, the head of the anti-gang squad of the Roman branch of the Italian State Police, is pursuing Emmanuel Dominique Ferrender, a French gangster who holds a monopoly on criminal activity within Rome.

Tanzi and his partner, Inspector Francesco Caputo, arrest Savelli but are forced to release him without charge; he later kills a guard during a bank robbery.

Maria Assante, the widow of a deceased colleague of Tanzi's, asks him to investigate the whereabouts of her teenage daughter Marta, who has fallen into an abusive relationship with drug dealer Tony Parenzo.

Having recovered from her ordeal and disillusioned with her career, Anna decides to temporarily live in Milan with relatives, which Tanzi agrees may be beneficial for their relationship.

To avoid further punishment, Tony attempts to convey key information about Ferrender, but he is shot dead by Moretto from a car driven by his friend Albino; they drive away just as Caputo and Anna arrive.

Tanzi soon discovers that the junkyard was once owned by Ferdinando Gerace, a businessman he had previously argued with over a lost license and encountered during his search for Marta, determining that he is a middleman between Ferrender and Moretto's gang.

Director Umberto Lenzi was offered a script titled Roma ha un segreto ("Rome Has a Secret"), a spy story set in the popular Roman district Trastevere.