A man is shot dead as he runs to catch the bus in the piazza of a small Sicilian town. Captain Bellodi, the detective on the case, is new to his job and determined to prove himself. Bellodi suspects the Mafia, and his suspicions grow when he finds himself up against an apparently unbreachable wall of silence. A surprise turn puts him on the track of a series of nasty crimes. But all the while Bellodi's investigation is being carefully monitored by a host of observers, near and far. They share a single to keep the truth from coming out.