Marshall (Judge Reinhold) works for a department store as a buyer, he is divorced and has a son called Charlie (Fred Savage) that he doesn't see very much at all.
On returning from his latest business trip abroad he finds himself in the possession of a very eerie looking, antique Eastern ornamental skull.
During one of his trips to stay with his father, Charlie soon discovers that this skull has some very special powers - it makes your wishes come true.
When Marshall and Charlie are talking (or arguing) the two simultaneously wish that they were each others age so that his father can go back to school and negate his responsibilities, and Charlie can leave school and work for a living.
In the presence of the skull, the two now change bodies, to the dismay of Marshall, but joy of Charlie.
Now they have their wish Charlie has to go to work and try and pass off as his father - and keep his job! While Marshall gets to go back to junior high.
In the hilarity that follows, Charlie also has to deal with Marshall's girlfriend. If that weren't enough a pair of smugglers are in pursuit of the skull.