Five years after leaving Libby sobbing and pregnant at the altar, Dennis must compete with the likes of Whit (Hank Azaria), a financial bigwig and marathon runner, for Libby’s affections. Joining Mary Poppins in the ranks of practically perfect in every way, Whit is everything Libby has ever wanted for herself and her son. He’s mature, considerate and responsible – all qualities Dennis lacks and all qualities that Libby claims are exemplified by Whit’s ability to train for and run a 26-mile race. And so the physically unfit, cigarette-sucking Dennis opts to compete in the marathon to prove that he, too, can be be mature, considerate and responsible. Dennis’s biggest hurdle? He only has three weeks to transform the flabby physique that gets winded by a sprint down the block into a lean, mean, marathon-running machine.

To give even more importance to Dennis’s completion of the marathon, both his best friend’s financial situation and his own current living situation rely on Dennis’s crossing the finish line. Best friend Gordon (Dylan Moran) has staked his entire savings on the race and Dennis’s landlord has agreed to forgive his back rent if he should accomplish his goal. Should he fail, Dennis faces eviction.

As Dennis, Pegg is affable in his ineptitude. He’s a subpar security guard at a women’s lingerie shop. He can’t afford to pay the rent in his tiny flat. And he’s ... well, he’s not exactly thin. But his obvious love for his son makes up for his inability to lead a successful life. And when the camera pans over his collection of pictures of him and Libby, it proves how much Dennis still cares for her. Too bad he isn’t funnier.

The tracking of Dennis’s training regimen – which makes up a significant portion of the movie – should be a primo opportunity for some comedy. And while there are funny moments, they come primarily from the presence of Dennis’s coach Gordon and assistant coach/landlord, Mr. Ghoshdashtidar (Harish Patel). In addition to Moran and Patel’s comic contributions, Azaria’s portrayal of the body-conscious, mostly flawless Whit is pitch perfect. Even though I knew I should be rooting for Dennis, a part of me saw why Libby chose Whit instead. Speaking of Libby, Newton is as bland as dry toast as the object of Dennis’s affection and the mother of his son.

Unfortunately, the new cast of supporting characters still don’t fuel the funny as much as Pegg’s usual comedic cohort, Nick Frost. Fans of Pegg’s previous efforts will quickly notice the obvious and lamentable absence of Frost. As Pegg’s bumbling sidekick, Frost provided the slovenly charm that worked so well when paired with Pegg’s good-natured straight man. Without the contrast of Frost’s oafishness, Pegg’s well-intentioned protagonist doesn’t possess the same likability.

The other element lacking in Run Fatboy Run is the direction and writing of Edgar Wright. Run Fatboy Run is helmed by David Schwimmer whose efforts are appreciated, but on the whole unsuccessful. Wright’s zany situations and over-the-top humor are sorely missed in this mostly mediocre movie. Dennis is a likable enough character, from his desire to make things right with Libby to his aww-inducing affection for his adorable son. But neither his dialogue nor his physical comedy are particularly hilarious. Having seen Wright and Penn’s previous collaborations, I expected uproarious laughter at almost every turn. Instead, I got the occasional giggle between predominately lackluster humor.