In a land down under, Ireland, a quaint, little island holds the family known as the O'Gradys. There's: Finnegan O' Grady, his wife Gail (who seems to believe everyone is going to burn in Hell), their bookworm son Flynn, and the boy's grandfather, Grady O'Grady, a man of the cloth.

One day, when Flynn is made to go into their chicken coop to clean out all the poop, he meets a giant, big, black snake with glowing, red eyes. Father Grady concludes that this creature is in reality the Devil, and he, the O'Gradys, and two volunteers, Mike O'Shea, and 95 year old Mrs. Mullarkey, must head out to the forest to find "the Beast."

On their journey, filled with banter, rants, comical violence, and a potato monster, they discover that the Devil is an Englishman (of course), and he wants to bring Hell to Earth by opening the Jaws of Hell. But to open them he must beat a human being in a contest of their choosing.

The Devil, using his tricks, tricks Flynn into agreeing to a fiddle contest, and thus begins a race to master this musical instrument. His grandfather, Grady O'Grady, teaches him how to play the fiddle, and through this journey, Flynn must dry his tears, miss much needed sleep, avoid temptation, and try to not be killed by a bloodthirsty mob, and worse.