Alfieri, an Italian-American lawyer in his fifties, enters the stage and sits in his office. Talking from his desk to the audience, he introduces the story of Eddie Carbone. Alfieri compares himself to a lawyer in Caesar's time, powerless to watch as the events of history run their bloody course.Eddie Carbone walks down the street to his house. As Eddie enters the home two fellow Longshoremen, Mike and Louis greet him. Eddie's niece, Catherine, reaches out the window and waves to Eddie and Louis. When Eddie enters the house he gently scolds Catherine for flirting with the boys so blatantly. Eddie thinks she should be more reserved and not "walk so wavy." Beatrice, Eddie's wife, is also home. While Beatrice and Catherine set the table for dinner, they convince Eddie to let Catherine take a job as a stenographer down by the docks. Eddie informs Beatrice that her cousins, Marco and Rodolpho, will be arriving early from Italy and will probably be at the house that night. Beatrice and Eddie plan to hide Marco and Rodolpho while they work in the country illegally to send money home.
Marco and Rodolpho arrive at the house and have a brief reunion. They are both very gracious for the hospitality. Marco tells the Carbone's that he has three children and a wife back home that he will be sending money to. Rodolpho, the young blonde brother, has no family and intends to stay in the country as long as possible. Rodolpho entertains everyone with his version of the jazz tune, "Paper Doll."
In the coming weeks, Rodolpho and Catherine spend a great deal of time together, which worries Eddie. Eddie thinks that Rodolpho is untrustworthy and Eddie becomes jealous of the time he spends with Catherine. Eddie tells Catherine that Rodolpho just wants to marry her to become a citizen, but she does not listen. Rodolpho develops a reputation at the docks for being quite a joker, which further embarrasses Eddie. Beatrice, more aware than ever of the attention Eddie is giving Catherine, talks to Catherine about being a woman and tells her she must grown up and make her own decisions. Beatrice encourages Catherine to get married to Rodolpho if that is what she wants to do. Catherine agrees to try. Eddie, still frustrated with Rodolpho and Catherine, even visits Alfieri and asks if there is any way he can get rid of Rodolpho by law, but Alfieri assures him there is not. Alfieri tells Eddie that he needs to let Catherine go.
The situation escalates and Eddie becomes increasingly jealous of Rodolpho. Eddie resents the fact that Rodolpho thinks Catherine is looser than Italian girls. Eddie threatens Rodolpho in a pretend boxing match held in the living room of the house, stopped by Catherine and Beatrice.
As Act II begins, Alfieri narrates and it is evident that time has passed. Rodolpho and Catherine are left alone in the house and have sex in the bedroom. As they are leaving the bedroom, Eddie comes home drunk. Eddie violently kisses Catherine, pins Rodolpho to the floor and kisses him also. Eddie visits Alfieri once again, who repeatedly tells him to let Catherine go. Immediately after leaving Alfieri's office, Eddie calls the Immigration Bureau and reports Marco and Rodolpho. Immigration comes and arrests Marco and Rodolpho. As he is being taken away, Marco spits in Rodolpho's face. Alfieri pays bail for the two men and arranges the marriage of Catherine and Rodolpho. On the wedding day, Marco returns to the house for revenge. Eddie lunges into Marco with a knife. Marco turns Eddie's arm and kills Eddie with Eddie's own knife. Eddie dies in Beatrice's arms.