Jessie McMullen (Sean Connery) is a Scotch-Irish American widower who immigrated to New York with his Sicilian wife in September 1946. With his charming yet roguish persona, Jessie is a proud former criminal who revels in his unruly past. He raised his son Vito (Dustin Hoffman) with the expectation that Vito would follow in his footsteps. However, at the age of 21, after the birth of his son Adam (Matthew Broderick), Vito chose to forsake a life of crime.
Now, Vito manages a successful wholesale meatpacking business on Twelfth Avenue, striving to leave behind the criminal associations of his youth. Determined to protect his son from the allure of their family's past, he marries a middle-class Hebrew woman and raises Adam in an environment steeped in conventional values. Yet, unbeknownst to Vito, his strict upbringing has the opposite effect; Adam becomes fascinated with his grandfather's enigmatic lifestyle.
As Adam nears graduation from college, he finds himself disillusioned with the future planned for him. Feeling constrained and longing for adventure, he flippantly drops out, stating he felt like he was being "put on a pension plan." In a misguided attempt to gain his grandfather's approval, Adam hatches a scheme for committing a burglary, much to Vito's dismay. In a moment of desperation, Vito confronts Adam in a bar, even striking him to emphasize the dangers of such choices.
Despite Vito's efforts to dissuade him, Adam's admiration for Jessie only deepens, and Jessie is eager to include Vito in what he claims is "the sweetest deal of my life.” As three generations of McMullens come together for this audacious plan, Vito reluctantly agrees to participate, seeing it as an opportunity to safeguard Adam.
The daring mission to steal valuable research from a lab unravels painfully when they realize Adam has forgotten the essential logbook. In a panic, Adam rushes back inside, inadvertently triggering an alarm. As Vito and Jessie watch helplessly, Adam is apprehended by the police, but not before he hurls the logbook to them, a desperate last act. Vito is devastated as Jessie remains composed, and together they manage to escape with the stolen goods.
Desperate to keep Adam out of prison, they hire a pricey lawyer who reveals that Adam's only chance to avoid a lengthy sentence is to betray his accomplices. Meanwhile, Vito's wife insists he confess alongside Jessie to help their son. It is then that they discover the scientific research was a sham, prompting Jessie to confront Adam's deceitful professor, Jimmy Chui, who had led Adam astray with the burglary idea.
In a moment of internal conflict, Vito ultimately decides to turn in both himself and Jessie, leading to a court that holds the three McMullens accountable. The judge hands Jessie a 15-year prison sentence, while granting Vito and Adam probation. Adam, disillusioned and consumed by anger, sever ties with Vito, labeling him a "piece of garbage" for betraying his father.
Tragedy strikes when Jessie passes away in prison just as Vito arrives to bid his father farewell, catching only a glimpse of Jessie's body being taken away. Overcome with grief, he grapples with the consequences of family loyalty and betrayal. In time, however, Vito and Adam reconcile, coming to terms with their shared memories of the family's escapade. Together, they honor Jessie with a grand farewell, recognizing the complexities of love and legacy steeped in their tumultuous history.
