Todd loves worms. He loves digging them up on the baseball diamond behind the school after it rains, loves collecting them in an aquarium in his basement, loves tormenting his sister Regina and her best friend Beth with them. Luckily his best friend Danny always gives him a hand in collecting worms, even though he doesn’t quite share his friend’s enthusiasm. Todd’s known as that kid who always wears the Raiders cap and loves worms.

Todd’s planning on entering a worm house in the Science Fair. The Worm House is a wood house with worms inside. Todd learns that Patrick, a rich blonde good-looking kid, is also entering a worm-related project in the Science Fair. Todd becomes obsessed with finding out what his project is, to ensure that his will be better than Patrick’s. Regina tells Todd Patrick’s address and Todd and Danny set off late at night to first meet with Patrick to try and get an answer from him, and then later when they see his mansion is abandoned, they decide to break in and see his project. Then an evil spirit dog chases them and they see a corpse inside the house and run away.

Todd overhears his sister the next day talking to Beth on the phone about what a great trick she played, sending the two boys to the abandoned mansion where some kids threw a Halloween party a few months ago. Todd gets revenge on her by putting worms in the beak of the paper mache bird she has created for the Science Fair, which she’s named Christopher Robin. Regina accidentally opens the bird’s beak when the Science Fair judges walk by and they land on the head of the judges.

Patrick sets his project down next to Todd’s modest worm house and reveals that he has built a massive worm skyscraper, complete with working elevators. The judges spend a considerable amount of time on Patrick’s project, mostly ignoring Todd’s. Todd is furious, especially since he’s the worm expert. He had even refused to let Danny help him with his project, leaving Danny to build a solar system representation made out of balloons, half of which deflate by the time the judges come around. The judges announce the winner of the Science Fair, Danny and his balloon solar system.

Todd goes back to digging up worms out by the baseball diamond. Danny and Todd have been noticing a low rumble every time they go out to the diamond to dig, and they even embarrassed themselves in front of the student body by proclaiming they were experiencing an earthquake.

Todd collects a bucket of worms and carries them back to his basement, where Regina and Beth are hanging out. Todd shows them a “neat” trick: he takes a worm and slices it in two. The two halves continue to wiggle forming two worms. Regina tells Todd that the worms in his fish tank are watching him, that they know what he did and they’re not happy, that they’ll take their revenge on him. The next day, Todd’s baseball cap is filled with worms.

Todd begins finding worms in his bed, his food, his homework, so on. He becomes so convinced that the worms are seeking their revenge that he sneaks down to the basement to apologize to the worms, where he’s caught by his father, who is wielding a baseball bat. Todd’s father tells him he has to get rid of his worms once and for all.

The next day at school, Todd walks to class in the pouring rain. When he enters the school, he and Danny overhear Regina telling her friends about how she’s been the one freaking Todd out, carefully placing worms all over his things to get him back for sabotaging her project. Todd drags Danny out to the baseball field to dig up worms after school. The rain has cleared and all the worms are coming out, the perfect time to grab some worms and get back Regina with them.

As Danny and Todd are digging around in the ground, they feel the rumble again and a giant worm the size of a tree trunk pops out of the ground, grabs Todd, and drags him underneath the soil of the baseball diamond. Danny waves at Regina and Beth, who are walking along the edge of the diamond, to help him. They are busy carrying their paper mache bird, the shadow of which falls onto the baseball diamond, casting the shadow of a giant bird. The giant worm sneaks back out of the soil, sees the bird shadow, and releases Todd from his grasp. Todd decides to abandon his worm hobby once and for all, and he begins to collect beautiful butterfly specimens instead, to the delight of his sister.

Todd is then awakened by a giant butterfly holding a huge silver pin who has shown up to take revenge.