After several years in prison, a recently paroled tough-as-nails--though not-quite-three-foot-tall--jewel thief Calvin Sims decides it's time to retire from a life of crime, but not before pulling off one last big heist. A notorious crime boss has offered Calvin and his former partner Percy P $100,000 to steal the famous Queen Diamond. The heist goes bad, and Calvin is forced to drop the jewel into Vanessa Edwards' purse. Vanessa and her husband Darryl then return to their suburban Chicago neighborhood unaware that they have become pawns in a high-stakes crime. Darryl and Vanessa are having problems of their own. Darryl is dying to assume the responsibilities of parenthood. But Vanessa, who has just been promoted to vice president at an advertising firm, is worried that having a baby will limit her ability to climb higher up the corporate ladder. When they overhear Darryl and Vanessa, Percy and Calvin devise a plan to exploit their insecurities in order to recover the stolen gem. Calvin will masquerade as a "baby," infiltrate their home and sneak away with the diamond. He deposits himself in a baby basket on Darryl and Vanessa's doorstep. Darryl leaps at the opportunity to prove he's ready for fatherhood by caring for the abandoned child for the weekend. To his surprise, Vanessa agrees. Once inside the Edwards home, the tough, cynical Calvin finds life as a "baby" to be a living hell and retrieving the diamond much tougher than he'd imagined.