Sonny Koufax (Adam Sandler) is an unreliable, unmotivated 32-year-old bachelor who lives in New York City and has declined to take on adult responsibility. He has a degree in law but has chosen not to take the bar exam since he was awarded $200,000 in a vehicle accident compensation years prior, and lives off his restitution. He is employed, on a part-time basis only, as a toll booth attendant, and more or less does this job just to get out of the apartment once in a while.
Meanwhile, Sonny's friends, all former schoolmates, are "moving ahead" in their lives. His roommate, Kevin Gerrity (Jon Stewart), decides to ask his podiatrist girlfriend Corinne (Leslie Mann) to marry him, which irritates Sonny, since he and Corinne dislike each other. Kevin decides to pop the question the day before he is leaving for China for his law firm. Two of Sonny's friends, Phil (Allen Covert) and Tommy (Peter Dante) are a homosexual couple in a committed domestic partnership, which surprised Mike (Jonathan Loughran), another friend of Sonny. Sonny's girlfriend, Vanessa (Kristy Swanson), disgusted and perplexed at Sonny's inconsistent conduct, decides to end her relationship with him—and also find a new much older man, Sid (Geoffrey Horne) with more reliability.
Kevin reveals to having fathered an illegitimate son, Julian McGrath (Dylan and Cole Sprouse). Sonny awakes to find Julian abandoned at his and Kevin's apartment, with a written explanation that Julian's mother is now declining to care further for Julian. It is later revealed at the Social Services Office that the boy's mother died of cancer. Kevin, at the airport ready to go to China, gets a call from Sonny, informing him of the letter and the boy. Sonny decides to handle the situation himself, and, in the process, decides Julian will solve his problem with his ex-girlfriend. His plan backfires when Vanessa rejects him, and Sonny ends up at Child Services, trying to give Julian back. Rather than give Julian to a group home, he decides to hang out with the 5-year-old boy until a new family is ready for him. In caring for him, Sonny discovers a new purpose in his life and a deep connection with Julian as a father figure. But Social Services rep Arthur Brooks (Josh Mostel) discovers that Sonny is posing as Kevin, and insists that he give up Julian. Brooks takes Julian and decides to press charges against Sonny.
The case is brought to court, where Sonny has his friends as counsel, including Layla (Joey Lauren Adams), Corinne's sister and Sonny's new girlfriend, and Kevin. Despite positive testimony from his friends and Corinne, a homeless man (Steve Buscemi) and his own father Lenny, also a prominent attorney, the judge is ready to sentence him to jail for kidnapping Julian and defrauding the state. At this point, Kevin steps forward as Julian's father and insists that no charges be filed, having remembered a drunken fling with a Hooters girl in Toronto during the 1993 World Series, and connecting that with Julian's earlier testimony of originally coming from Toronto and being born in July. The judge grants custody to Kevin to the dismay of Julian, who wants Sonny as his father. Sonny tells Julian that can never happen because his real father is present, but they can be friends.
One year, three months, and six days later, Sonny, now a lawyer and married to Layla with a child of their own, is surprised with a birthday party at Hooters attended by all his colleagues and friends, including Julian, but is more surprised to find Vanessa working as a Hooters girl, and her boyfriend Sid, working the grill, apparently not as rich as Vanessa had thought him out to be.