Russ Duritz (BRUCE WILLIS) is a successful, high-powered image consultant who's single and about to turn forty. Self-centered and ruthlessly straight to the point, Russ is good at what he does, but has few friends or even time for his father, Sam (DANIEL VON BARGEN), or other relatives.
Despite Russ' cool demeanor and lack of emotional depth, both his secretary, Janet (LILY TOMLIN), and personal assistant/sometime girlfriend, Amy (EMILY MORTIMER), stick with him, only serving to reinforce his behavior. That's about to change, however, when he suddenly has repeated encounters with Rusty (SPENCER BRESLIN), a somewhat awkward and pudgy eight-year-old boy.
It's not long before Russ and Rusty realize they're the same person, but at different ages, a point that scares the boy but cracks up the businessman as he believes he's experiencing his first mental breakdown. When Janet confirms that Rusty is real, however, Russ realizes he has a bigger problem. With the boy representing a childhood he worked hard to suppress, Russ tries to figure out the reason behind Rusty's sudden appearance. Meanwhile, the boy isn't happy to learn that at the age of forty he'll be a man without a wife, dog or a job as a pilot. In other words, he's grown up to be a loser.
Realizing that he can help Rusty - with the help of his friend, Kenny (CHI McBRIDE), the heavyweight champion of the world - while helping himself, Russ tries to remember his childhood and one certain pivotal moment from the past that can not only help return Rusty there, but may also be the key to help the busy businessman regain his inner child, become a better person and make amends with Amy.