Sonny Koufax, played by Adam Sandler, is a laid-back and aimless 32-year-old bachelor living in the bustling metropolis of New York City. Earning a law degree but choosing to avoid adult responsibilities, he relies on a hefty $200,000 settlement from a past car accident to support his lifestyle. Currently, he holds a part-time position as a toll booth attendant, a job he only keeps to escape his apartment occasionally.
As the film unfolds, we witness Sonny's friends, once his schoolmates, making significant strides in their lives. His roommate, Kevin Gerrity (portrayed by Jon Stewart), is preparing to propose to Corinne, played by Joey Lauren Adams, adding to Sonny's growing irritation. Kevin plans to pop the question just before leaving for a work trip to China, but Corinne can't stand Sonny, continually reminding her of her days working at Hooters while studying medicine.
In a notable turn of events, Sonny's relationship with his girlfriend Vanessa (Kristy Swanson) takes a nosedive as she grows frustrated with his immature behavior and decides to seek a more stable partner. Suddenly, Sonny finds himself entwined in a whirlwind of unexpected responsibilities when he learns that Kevin has a son, Julian (a dual role by Dylan and Cole Sprouse). Julian is dropped off at their apartment with an explanatory note about his mother, who has tragically passed away from cancer.
Promising to look after Julian until Kevin returns, Sonny naively tries to utilize the boy in a plan to win back Vanessa, but soon realizes she is now with Sid, an older man whom she sees as more structured and ambitious. Frustrated with the challenges of fatherhood, Sonny takes Julian to meet Arthur Brooks (Josh Mostel), their social worker, under the guise of Kevin, only to learn that Julian is now in need of foster care.
Sonny embarks on an unexpected journey of self-discovery as he begins to bond with Julian, uncovering a newfound purpose as a father figure. With Julian's influence, Sonny also develops a connection with Layla, Corinne's sister and his new love interest. However, as social services become aware of Sonny's deception, they threaten to remove Julian from his care altogether, leading to a court case where Sonny's friends, including Layla and surprisingly Corinne, come to his aid, offering positive testimonies.
In a dramatic courtroom scene, Sonny even takes the stand, convincing his father, Lenny, of his readiness to raise a child. When Kevin admits to being Julian's biological father, the judge grants him custody pending DNA results. Despite the outcome, Sonny vows to remain a part of Julian’s life, maintaining their bond through regular meetups.
Fast forward a year, and Sonny has grown significantly. Now a lawyer, married to Layla, and with a child of their own, he is taken aback at a surprise birthday party at Hooters, where he sees Julian again, alongside his colleagues. In a humorous twist, he also spots his ex-girlfriend working there, serving up laughter and nostalgia as he embraces his new life, forever changed by the adventures that unfolded.
