Hubert Flynn from Dublin loves his pint of Guinness, his bet on the horses and his wife Conchita, in that order. So when he comes home from the pub one evening and changes into a rat, she is slow to forgive. His children have differing views. His loving daughter Marietta wants to give him the special care and attention a small rodent requires, but she is engaged to be married and wonders how he will cope as father of the bride. His son Pius, destined for the religious life, wants to put him in the oven. Conchita resists, but when Phelim Spratt, an opportunistic ghost-writer, knocks on the door and proposes telling Hubert's story in a book, then a film of the book, then maybe a book of the film... she is tempted. But in this Irish fable of family values and little furry folk, there are lessons to be learnt for everyone before love triumphs and the rats come home to roost.