Run, Fatboy, Run

Pegg plays Dennis, a likeable loser who got cold feet on his wedding day and ran out on his bride-to-be, Libby (Thandie Newton). The action in RUN, FAT BOY, RUN takes place five years after this event. In the preceding years, Dennis has landed a job as a lowly security guard and Libby has given birth to a son, Jake (Matthew Fenton), who was conceived with Dennis before their break-up. Libby has also hooked up with a new man, the slimy but successful American businessman Whit (Hank Azaria). Dennis, who is still hung up on Libby, decides he must compete against Whit in the forthcoming London marathon to win back her affections. But, naturally, things don't quite go according to plan. (official distributor synopsis)