The fatboy of the title is Dennis (Pegg of course). We find him sweating profusely and considering his limited options as his pregnant bride-to-be Libby (the lovely Thandie Newton) waits at the altar. Dennis' final decision: run! Run as fast as he can away from responsibility and commitment. Five years later the film finds Dennis is still running. He's trying to rundown a shoplifter from the lingerie store where he works and it's not a pretty sight. But he hasn't run entirely away from responsibility. We discover that he has maintained contact with his son, who is now five, and is at least trying to be a presence in his life.