Plot

Five years after jilting his pregnant fiancée on their wedding day, out-of-shape Dennis decides to run a marathon to win her back.

Dennis is a clueless and slightly overweight guy, who left his pregnant fiancée five years earlier. Every day, Dennis tries to persuade the woman he loves to accept him back into his life, but everyday he fails. When he discovers that Libby has found a partner in the form of American Whit, frustration grows, and Dennis vows, that for once in his life, he will finish something. This something ends up being a Nike River-run in London. With his friends Gordon and Mr. Ghoshdashtidar by his side, Dennis begins training for the marathon he must finish.—FilmFanUK

Clumsy, lazy London boutique security guard Dennis left Libby, the mother of doting and adored five year-old Jake, at the altar. Now that she has a new lover, hunky American business executive Whit, who takes an active interest in the boy, Dennis fears to loose Jake. Hearing Whit is training for another marathon, Dennis hopes to prove himself worthy. Getting fit would fail utterly, hadn't his dodgy mate Gordon wagered on him against his dangerous gambling debts, while Dennis's Indian-roots landlord Goshdashtidar volunteers as 'assistant coach', armed with a motivational ladle. It's a miracle they even get Dennis registered, too late, needing a sponsor. That done, the race proves eventful, and reveals Whit isn't as perfect as he looked naked in a gym locker-room as well as an engagement party.—KGF Vissers

U.K.-born Dennis Doyle is in love with Elizabeth Odell, both get intimate, and when Elizabeth gets pregnant, plan to get married. On the day of the marriage, Dennis gets cold feet at the 11th hour and flees. Five years later, Dennis regrets this decision and attempts to re-enter Elizabeth and his son's lives encouraged by his friends, Gordon, and Goshdashtidar, a Londoner originally from India. He decides to impress her by participating in a marathon-run in London. Before he could even act further, he finds out that Elizabeth has an American boyfriend, Whit, who proposes to her - and she accepts. Watch what impact this has on a visibly overweight Dennis' decision to continue to participate in the marathon-run.—rAjOo (gunwanti@hotmail.com)

A chunky, clueless guy leaves his pregnant fiancée on their wedding day only to discover -- 5 years later -- that she is his one true love. But in order to win back her heart, he looks to finish his first marathon while making her realize her new man is the wrong guy for her.—Anonymous

Dennis Doyle (Simon Pegg) is about to marry Libby (Thandie Newton), his pregnant fiance. However, he gets cold feet and runs away on the day of the wedding. Five years later, Dennis discovers that Libby, who has their son, Jake, has started seeing high-flying and ambitious Whit (Hank Azaria) and realizes what he has lost. He finds out that Whit is running the Nike River Marathon in London, and to prove himself to his doubting friends and, most importantly, Libby and his son, he decides to run the race himself. He receives motivation from his two "coaches", Gordon (Dylan Moran), Libby's cousin and Dennis' best friend who has made a hefty bet on Dennis succeeding, and Mr. Ghosh Dastidar (Harish Patel) his landlord, who uses unorthodox methods of training, such as using a spatula to spank him.

Days before the race, Whit proposes to Libby at her birthday party. Libby accepts and this puts Dennis in a state of depression. Meanwhile, Jake, who has formed a crush on a girl in his class, runs away angry when he discovers that she prefers another boy just because he has a ponytail. Dennis, upon being informed by a frightened Libby, tracks him down and explains to him that he will find many things he does not like in his life, and he should just stand up to them and face them, rather than running away. Having made that mistake himself, he decides to race after all.

Dennis starts the race alongside Whit, who informs Dennis that he intends to move Libby and Jake to Chicago, Illinois. Angered, Dennis insults Whit and they tussle for a while at the start of the race and, in their efforts to out-do each other, they catch up to and then overtake the professional runners, and suddenly Whit trips Dennis and badly injures him. Stretchers prepare to take Dennis to the hospital. Whit continues but is taken to the hospital after feeling ill and feeling pain in his leg.

Libby goes to the hospital to find Dennis, but only finds Whit, who claims loudly that his injuries are the result of Dennis deliberately tripping him. The doctor tells him he is not actually injured and has only "hit the wall". Whit, in a fit of anger, calls Jake a "little s**t" because Jake played with Whit's hospital bed, to Libby's horror.

Dennis has in fact refused to be transported to the hospital or even get medical attention and is continuing the race well into the afternoon and evening with a sprained ankle, accompanied by a growing group of supporters, including Gordon and Mr. Ghosh Dastidar. An exhausted Dennis almost "hits the wall" but after an emotional inner struggle, his resolve to complete the race is restored.

Later at Whit's house, Libby, Jake, and Whit, watch a television replay of the Whit/Dennis tussle, as the replay shows that in fact Whit had deliberately tripped Dennis up and had fallen over because he had gotten tangled up with Dennis as he was falling. As Whit tries to justify his behavior, he blurts out his intentions to have Libby and Jake move to Chicago with him. A furious Libby puts the engagement ring on a table, telling Whit "nobody's perfect" and storms out with Jake. The two go to meet Dennis as he arrives at the finish line. Dennis falls over just meters from the finish line and cannot get up until he sees Libby and Jake calling to him at which point he gets up, sprints to the finish and collapses in their arms.

Sometime later, notably slimmer and no longer limping, Dennis calls at Libby's house to pick up Jake. He says that he has something to ask her, but is interrupted by Jake, and says he'll talk to her later. However, just after she shuts the door, he knocks again and asks her on a date. She accepts.

In the film's postscript, Gordon - on the bridge of a new yacht - tells the tale of the race to two attractive bikini-clad women, whom he invites aboard for a drink. The camera then pans to reveal to the audience that he's again naked below the waist.