Tony Breda, a respected yet small-time criminal in his Italian town, idolizes the Italo-American mobster Frankie Diomede, nicknamed Dio. After reading in the paper that Dio has returned to Genoa to take care of a rival organization led by Louis Annunziata, Tony tails him from a hotel to a villa party and tries to gain entry. Dio calmly calls the police and exposes illegal gambling at the party, effectively arranging his own arrest. As the sirens draw closer, Tony pushes through the fleeing guests in a bid to rescue him, believing that saving Dio will secure him a life in crime, but Dio refuses to depart and both men end up in custody.
While behind bars, with a guard who has presumably been paid off, Dio slips out at night to murder a rival. When he returns, Tony witnesses the act, and Annunziata alerts the police to the murder, triggering a broader investigation. Tony learns that he will likely spend a couple of weeks in jail on minor charges, and he tries to win Dio over with flattery and imitation, but Dio largely ignores him. A tense moment arrives when Tony spots an assassin with a sniper rifle on a prison roof and pushes Dio out of the line of fire, saving his life. Dio softens toward Tony, who proclaims he would do anything for him.
Dio asks his estranged brother, a respectable doctor, to visit him and hand over files containing information on the rival organization to the police. The brother agrees but is followed, pulled into a photo booth, and murdered; a gang member uses the booth to take a photo of Dio’s dead brother. Tony convinces Dio that a breakout is possible during Dio’s transfer to another prison, and he orchestrates it by staging a car crash and signaling for a police car transporting Dio. The two then embark on a dangerous police chase in a truck filled with oil drums, crossing the border into Marseilles.
In Marseilles, Dio tracks down his rival at a fish processing warehouse, where Annunziata’s outfit hides heroin inside gutted fish destined for the United States. A brutal shootout erupts, and Tony proves useful, though he is paralyzed by distress after firing at a man he believes he has killed. Dio reassures him that he did not kill the man. He then forces Annunziata at gunpoint into a cold storage room and lowers the temperature to its lowest setting, causing Annunziata to freeze to death. Dio arranges a boat to Tunisia, telling Tony that a life of hard crime is not for him and urging him to reform his ways. Tony accepts that he is not cut out for such violence and returns home. When he greets his friends, they read an unfavorable newspaper excerpt about Dio, and Tony urges them to choose an honest life.
