In Thailand, a pair of thieves steal an ancient skull from a Buddhist monastery.
Marshall Seymour [William Prince] is vice president of a Chicago department store. He is divorced and has an 11-year-old son named Charlie [Fred Savage], for whom he has little time. He and his girlfriend Sam [Swoosie Kurtz] visit Thailand to purchase exotic merchandise. At the same time, an art thief named Turk [David Proval] must find a way to smuggle an ornate skull out of the country. He places it with one of Marshall's purchases so that he and his accomplice Lillian Brookmeyer [Corinne Bohrer] can make a switch later.
When Marshall returns home, he takes Charlie for a few days while his mother Robyn [Jane Kaczmarek] and stepfather Cliff [Judge Reinhold] are on vacation. While holding the skull, they wish that they could be in each other's bodies. The skull possesses magical powers, and they suddenly find that they have switched bodies.
The two realize they must live out their lives as each other. Marshall heads to school, while Charlie assumes his father's role as a vice president.
Marshall and Charlie visit the museum and talk with Professor Kerschner, who explains the true nature of the skull and wishes to show it to a lama before returning it to them. Robyn arrives home earlier than expected and is furious at the sight of Marshall (as Charlie) drinking a martini.
After failing to reacquire the skull, the thieves embark on a mission to steal it. Charlie learns from Marshall's boss Avery that he has called a meeting to pull the plug on Marshall's business. He collects Marshall at school and, after purchasing a device that will allow them to communicate with each other, Marshall listens in on the boardroom meeting and instructs Charlie on what to say. However, Turk kidnaps Marshall, leaving Charlie to fend for himself in the boardroom.
With Turk and Lillian holding Marshall for ransom, Charlie retrieves the skull from the lama. He then exchanges it for Marshall. However, he and Charlie rush to reacquire the skull so that they can switch themselves back. They catch the thieves just after they have accidentally switched bodies, and they take the skull back, leaving Turk and Lillian in their new bodies as punishment.
The police arrest Charlie for possible kidnapping, so Cliff posts his bail. Marshall asks Sam to take him home so that he can give Charlie a present. On the way, he proposes marriage.
Charlie and Marshall touch the skull, switching back into their own bodies. Marshall then goes to see Sam while Charlie listens to their conversation about the proposal. Though initially caught off guard, Marshall relents and embraces the proposal that Charlie made for him.
