Kevin Franklin (Sinbad) is an inner-city Pittsburgh native; raised in an orphanage, he has delusions of grandeur and talks about one day getting rich and driving a Porsche. 25 years later, Kevin drives a rusted MG Midget and all his ambitions revolve around a series of ill-fated get-rich-quick schemes. A handshake loan of $5,000 from the mob grows to $50,000 through interest and penalties, resulting in his trying to skip town at Pittsburgh International Airport. Kevin overhears a conversation between lawyer Gary Young (Phil Hartman) and his wife Emily (Kim Greist), who are waiting to pick up Young's childhood friend Derek Bond, who is now a successful, straight-laced and vegetarian dentist. Upon hearing Young say that he hasn't seen Bond in 25 years and doesn't know what he looks like, Franklin gives his ball cap to the real Bond to throw off the two dim-witted mobsters chasing him and poses as Bond to the Youngs, who take him to their posh home in Sewickley.
Although he knows nothing about dentistry, Franklin still manages to convince those around him that he is in fact Derek Bond, and his affable personality makes him popular with Young's otherwise stuffy and rich neighbors and associates. Young has little time for his children and his wife's new frozen yogurt business, which gradually builds a gap between them, largely due to the demands of his bigoted, arrogant boss (Mason Adams) at the law firm where he works; this leads to Franklin developing a bond with Young's Goth daughter, helping her stand up to her cheating boyfriend, and his young son, who has aspirations of playing pro basketball. Young eventually stands up to his boss with Kevin's support and quits the firm to be with his family. Meanwhile, the mob thugs threaten Kevin's best friend Larry (Stan Shaw) into revealing his whereabouts, and Franklin asks Larry to pick him up when tensions in the house run high.
After Larry does so reluctantly, he sparks an argument with Kevin over his lack of appreciation of friendship, causing Kevin to realize that Young has been his friend all along. He returns to the family only to find that the mobsters have taken them hostage, and Kevin's true identity is revealed when the real Derek Bond finally shows up. After the mobsters take Kevin away, he manages to escape, and loses them in a charity marathon, where he meets up with Young, who graciously decides to help Kevin despite his charade, in return for helping bring Young's family closer together. Kevin reveals that he has an instant lottery ticket he purchased the previous day for a chance at a $1,000,000 cash prize spin on a Saturday night TV show, which he reluctantly gives up to the mobsters in exchange for the forgiveness of his debt. Some time later, Kevin parallel parks a shiny new red Porsche in front of the Young household, appearing for a promotional party for his new best-seller book "Handbook for Houseguests", based on his experiences with the family.
The partygoers gather in front of the TV to watch the mobsters spin the wheel for the jackpot. The wheel initially lands on the million dollar jackpot, but then falls and lands on $5000, much to the mafia don's dismay. During the closing credits, Hartman and Sinbad sing a medley of food-based parodies of Christmas songs..