Dublin deliveryman Hubert Flynn feels peaked. Home from the pub, he lies down; while his nagging wife Conchita looks on, he turns into a rat. She's chafed at how inconsiderate he is: hardly touching his food the next morning and leaving droppings on the good doilies. With curiosity seekers outside the flat and a writer at the door offering to help Conchita turn her story into a book, she calls a family meeting. Her seminary-bound son Pius wants to kill the rat; other family members are ambivalent. They opt to hurl Hubert over the fence of a maggot farm. Christmas approaches; an exorcism is in the cards, and the book becomes the Holy Grail. What of Hubert's conversion?