Russ Duritz (Bruce Willis) is a wealthy Los Angeles based image consultant, but as he nears 40, he's cynical, dogless, chickless, estranged from his father, and he has no memories of his childhood and is deeply unhappy with himself.
One night, however, he surprises an intruder, who turns out to be a kid of just 8 years old, but there's something oddly familiar about this chubby little lad, whose name is Rusty.
This boy's identity sparks a journey into Russ's past as he realises that Rusty is in fact him when he was eight and has been sent forward in time to help his older self get in touch with who he used to be. Now the two of them try to find the key moment that has defined who Russ really is.
Two long-suffering women look on with disbelief: Russ's secretary, Janet (Lily Tomlin), and his assistant, the lovely Amy (Emily Mortimer), to whom Rusty takes a shine.
What, and who, is at the end of this journey?