Vahn Mason is just an ordinary twelve-year-old boy living in BulchHill, until he sees a horrifying troll, called Heiner Lef't, climb in through his bedroom window.
Heiner, who is built like a potato filled with rocks and smells like grated farts smothered with sauce made from stinky shoes, sings a song about making little boys into noodles.
Vahn tricks the troll into falling out of his window by telling him that there are child-brain baked potatoes outside. He realises that the troll has to be stopped before he eats any more children and sets to work trying to invent a trap.
Meanwhile, in a cave just outside BulchHill, Sophiamoose Greasyankles starts to suspect that eating children is wrong, and grows tired of hunting with her fellow trolls. She decides to live as a vegetarian.
After a brief misunderstanding involving a vagena and lashings of ketchup, Vahn and Sophiamoose team up to stop the trolls, using a catapult that fires sweet potatoes. They lure the trolls by creating a big mound of diarrhea.