The game begins with Thomas “Tommy” Angelo entering a bar to speak to police Det. Norman. After announcing that he wants to be in the Witness Protection Program, Tommy proceeds to tell the story of how he got involved with a crime family headed by Ennio Salieri, providing the story’s main narrative.
While working as a cab driver in fictional Lost Heaven in 1930, Tommy picks up two mobsters, Sam and Paulie, who force him to help them lose two mobsters working for Salieri’s rival, Don Morello. After losing them and delivering the two to their boss’ place, Tommy is rewarded a large amount of money. The next day, while taking a break, Tommy is attacked by the thugs he helped Sam and Paulie escape from. Though he is saved by Salieri’s men, he subsequently loses his job. Desperate to make money, Tommy falls in with Salieri’s crew and gets involved in all his criminal operations.
Over the next 8 years, Tommy does big jobs for the family, such as murdering other gangsters, entering races, stealing, bootlegging (this is during Prohibition), robbing banks, and property destruction. He slowly rises through the ranks as the jobs get bigger, such as when he has to kill Salieri’s double-crossing consigliere. Eventually, the rivalry between Salieri’s crew and Morello’s crew erupts into a war. This is where Tommy gets his biggest job: assassinating Morello, ending the feud once and for all. During this time, Tommy falls for and marries Sarah, daughter of Salieri’s bar’s bartender, Luigi, with whom he eventually has a daughter of his own.
Tommy’s story reaches its climax when, in 1938, he and Paulie (whom, along with Sam, he’s become close friends with) learn that Salieri’s been smuggling diamonds in secret and keeping the profits for himself. Deciding to get back at him, they rob a bank (Sam refuses). Though the heist is successful, Tommy finds Paulie shot dead the next day. Sam calls Tommy and asks that he meet him at an art gallery. There, he learns that Sam ratted him and Paulie out to Salieri, who ordered their whacking. After a shootout, Tommy manages to kill Sam and several others. He then flees to Europe with his family, but quickly returns to set up the meeting with Norman.
His story over, Tommy makes his demands: in return for immunity for his past actions and protection, he’ll testify against his former comrades. In the trial that ensues, 80 gangsters are tried, most are executed and Salieri gets life in prison. Tommy and his family are put under federal protection and remain safe for 13 years. However, in 1951, his past fatally catches up to him as he is shot dead by two gunman. The game ends with Tommy lamenting in voiceover the mistakes he made, saying that in wanting it all, he eventually lost everything.

Mafia: The City of Lost Heaven