Pete Postelthwaite is Hubert Flynn, a bread delivery man who loves his Guinness and horse racing more than his wife, and who one night comes home from the pub to discover that he has been turned into a rat. His wife Conchita (Imelda Staunton) is not impressed. She does not forgive easily and refuses to take pity on him. But when a ghost-writer knocks on the door offering Conchita to put their story into a book and then a film of the book and then a book of the film, she is sorely tempted to cash in. This sets the stage for a series of comical adventures for Hubert the rat.