In 1984, 13-year-old Donny Berger finds himself entangled in a scandalous affair with his teacher, Mary McGarricle (Eva Amurri Martino). Their relationship takes a dramatic turn when they are caught engaging in a sexual act on a piano during an assembly, resulting in Mary facing a lengthy prison sentence and the shocking revelation that she is pregnant. Custody of the child, whom Donny whimsically names Han Solo Berger, is given to Donny's abusive father until Donny reaches the age of 18. During this time, Donny becomes a media sensation, capturing headlines and hearts as a teenage idol, appearing on numerous talk shows and magazine covers.
Fast forward to 2012, and we find Donny (Adam Sandler) living a disheveled life as a broke and drunken slacker. His days are spent hanging out with his friends, including bartender Brie (Ciara) and stripper Champale (Luenell). Meanwhile, his son, now known as Todd Peterson (Andy Samberg), has distanced himself from Donny due to the embarrassment of his father's reckless behavior. Todd, a successful businessman, is preparing for his upcoming wedding to Jamie Martin (Leighton Meester) at his boss's Cape Cod estate, while dealing with the added tension from Jamie's brother, Chad (James Caan), a no-nonsense military man.
Amidst this chaos, Donny learns from his lawyer, Jim Nance (Rex Ryan), that he owes a staggering $43,000 in back-taxes and faces a three-year prison sentence unless he can pay by the weekend. In a desperate move, he contacts TV producer Randall Morgan (Dan Patrick), who offers him $50,000 to orchestrate a reunion with Todd and Mary in prison.
Arriving at Cape Cod, Donny attempts to reconnect with Todd, introducing himself as an old friend to cover up his true identity. Despite his crude behavior, Donny's colorful storytelling earns him a quick rapport with everyone, much to Todd's chagrin. Donny tries to persuade Todd to meet his estranged mother under the guise of a serious medical condition, but Todd remains resistant. The growing tension leads to confrontations, as Todd grapples with the realization of Donny's failures as a father, both in the past and present. Donny, reflecting on his upbringing, admits he struggled to learn how to be a father himself.
As the story unfolds, Todd becomes increasingly influenced by Donny, which culminates in a dramatic incident at church where a fistfight with Father McNally (James Caan) causes the wedding rehearsal to be canceled. Donny intervenes to save Todd from further humiliation, moving the venue to spare him the embarrassment of the explosive confrontation tied to their traumatic past.
The bachelor party that Donny crashes leads them down a path of indulgent recklessness—drugs, alcohol, and debauchery push Todd closer to his father, as the two forge an unexpected bond. However, when it comes time to meet Mary in prison, Donny's intentions conflict with Todd's genuine desire for closure, resulting in yet another emotional setback when the TV crew catches them off guard.
Complicating matters further, Donny learns that Jamie is involved in an affair with Todd's boss, which he grapples with disclosing to his son. After discovering Jamie in a compromising situation with Chad and realizing the stakes, Jamie attempts to silence Donny with a $50,000 hush money offer. However, the heartfelt gesture from Todd in the form of a gift—the oven mitt he once cherished—leads Donny to reject the money, igniting his determination to prevent the wedding.
With a cameo from Vanilla Ice, Donny races to the wedding, determined to reveal the truth. He publicly acknowledges himself as Todd's father, tearing up Jamie's check and exposing her to Todd. Faced with this revelation, Todd breaks off the engagement and reclaims his identity as Han Solo Berger.
The next day at a strip club, Han confides that he is dating Brie and offers to assist Donny with his tax troubles. But Donny, opting to take responsibility, declines the assistance. As he prepares for his impending incarceration and a potential rekindling with Mary, fortune smiles upon him when a bet turns in his favor, granting him enough money to settle his debts with the IRS. The film concludes with Donny and Han celebrating this newfound freedom, surrounded by friends, a testament to their evolving relationship.
