Five years ago Dennis (Simon Pegg) was at the altar about to marry Libby (Thandie Newton) his pregnant fiancé. He got cold feet and ran for the hills and he s been going in circles ever since. When Dennis discovers Libby s hooked up with high-flying-go-getter Whit (Hank Azaria) he realizes it s now or never. He enters a marathon to show he s more than a quitter but then finds out just how much sweat strain and tears it takes to run for 26 miles. Nobody gives him a chance but Dennis knows this is his only hope to be more than a running joke.