The cover illustration featured an muddy monsters in the muddy swamp.
Eddie Campbell is on a class field trip out in a forest with many of his classmates. Among his friends are Hat, which is the nickname of a boy who never takes off his hat; Molly and Charlene, two girls who are described as interchangeable and indeed, they are. All four of these children loathe the class show-off, Courtney King. On the field trip, Eddie is embarrassed or one-upped by Courtney several times. First she spots a deer. Then she teases Eddie for being scared of a garden snake. Then the class crowds around Courtney, as she lets two bumblebees walk across her palm. Then, she takes the bees and throws them at Eddie.
On the bus ride back, the quartet of friends discuss how Courtney and her best friend, Denise, never seem to be afraid of anything. As the bus drives past the muddy forest, Eddie wonders if she would even be scared of the fabled Mud Monsters that supposedly live in the forest. His older brother Kevin is making a movie about the legend of the mud monsters in his spare time, starring his friends.
After the field trip, Eddie begins a slow descent into obsession, eventually dragging all his friends with him as he becomes infatuated with the idea of getting Courtney back. First Eddie and his friends come up with placing a rubber snake in Courtney's lunch bag. Their schoolteacher, Mr. Melvin, forgot his lunch that day, and Courtney being the nice person she is, kindly offers to share her lunch with him. The teacher reaches into the bag and freaks out at the snake. Courtney heroically stomps on the snake until she has torn the head clear off.
On the way home after that failure, Eddie and his friends are approached by a neighbor lady. Her cat is stuck in a tree and she needs help rescuing it. Eddie contemplates climbing the tree, but decides he is not comfortable with the safety issues. At that moment, Courtney rides by on her bike, sees the situation, shimmies up the tree and rescues the cat for the neighbor. The neighbor then rubs it in by chastising Eddie for not being brave enough to climb the tree.
As they leave the neighbor, the group comes up with another plan to scare Courtney. Eddie and Hat will sneak into the school’s science lab, steal a tarantula, then race up to the rafters of the gym. Down below, Molly and Charlene will get Courtney to stand directly below the balcony, and Eddie will drop the tarantula into her hair.
Eddie and Hat sneak into the science lab to steal the tarantula. They place the creature into a cottage cheese container. But as soon as they close the lid, they hear the science teacher entering the lab. They both hide inside a storage locker as they hear the teacher milling about in the room. At this point Eddie notices the lid of the container is open and the tarantula is climbing up his leg. He and Hat both freak out and as soon as the teacher leaves, they discover the locker is locked. Eddie bursts out of the locker and the tarantula goes flying across the room. There is a mad dash race by Hat to capture it back into the container.
From the rafters, they see Courtney is finally in place below them. Hat opens the container and drops the tarantula... into Molly's hair. She freaks out and tears at her head, finally removing the spider and tossing it into the air, where it lands in Charlene's hands and she bats it about like a hot potato. Finally, Courtney calmly takes the creature in her hands and pets it, telling the bystanders that tarantulas aren't all that scary. Eddie and Hat are caught and sentenced to detention, where they are forced to write a 1,000 word essay on why "It's wrong to steal living things and drop them on people's heads."
Eddie's fiery desire to see Courtney get scared continues to eat away at him. He asks his film making brother for tips on how to scare her. He points out that a snake and a spider are too small and Eddie needs something big. Like a ferocious, angry dog.
Eddie runs this idea past his friends the next Saturday afternoon. Charlene suggests that Buttercup, her cuddly St. Bernard, could do the trick. The others are less than convinced and the name does nothing to help her argument. So Charlene shows them a trick that involves whistling until the dog snarls and bares its teeth and looks very menacing. When Charlene stops whistling, the dog returns to normal. Eddie is floored and wants to put the idea into motion immediately. He knows that Courtney and Denise had a tree house built near the creek and that if they were out relaxing in the forest and suddenly a wild dog attacked, they would surely be scared.
But how to get Courtney into the forest? Molly surprises her friends by changing her voice and pulling off a perfect impression of Denise. She will call Courtney up and pretend to be her and arrange for the two to meet at the tree house. This plan does not work so well, as when Molly calls pretending to be Denise, Denise is already standing next to Courtney.
A week goes by, before the weather allows for them to try to catch Courtney off-guard in the forest. The gang treks out into the forest, merely hoping that Courtney and Denise will be at their tree house, and as luck should have it, they are. Eddie takes some shaving cream out and smears it on the dog's jaw to make it look rabid. Charlene is about to whistle, when Buttercup sees a squirrel and goes running off into the thicket after the animal. The group of friends splits up to search for the dog. Eddie hears a dog growl and turns around to see a giant, pony-sized black dog with coal-burning eyes. Hat shows up and scares the giant beast away. As the four exit the clearing, they spot Courtney calmly playing with both Buttercup and the mysterious beast dog, who is licking her hand. Courtney gives them a lecture about letting their pet go wild in the forest.
The following week, Eddie and his friends lie to their parents and claim to be studying, but instead sit around and think of ways to scare Courtney. No decent ideas come to fruition, but on the way home, Eddie gets spooked by the wind, and gets an idea when he realizes that the reason Courtney was not getting scared was because they kept attempting to scare her during the day. They need to scare her at night.
At school the next day, Courtney tells her teacher that she believes in monsters. She gives proof, such as the photographs of the Loch Ness Monster and the footprints of Bigfoot. Eddie uses these comments to think up a new idea. Eddie agrees to be his older brother's slave for one month, if Kevin and his friends will dress up in their mud people costumes and scare Courtney in the forest. He agrees and Eddie tells him to go out into the forest. Now all Eddie and the gang need to figure out is how to get Courtney into the forest. Molly calls her and challenges her to meet them in the forest to see the mud monsters. Molly tells Courtney that she heard on the radio that they would be rising up from their muddy graves tonight. Courtney takes this as truth and agrees to be in the forest in ten minutes to prove she is not afraid.
We're then given a brief history of the legend of the mud people. Once upon a time there were two neighboring villages, one in the forest and one in the city. The city village hated the forest village and treated the villagers poorly. One stormy night, a rainstorm caused the creek in the forest to overflow and flash flood, burying the entire village in a mudslide, killing all the villagers. Local legend claims that once a year, the townspeople return to form, covered in mud, and go to find innocent victims to drag back with them into the mud.
The four friends hide about 100 yards behind Courtney's tree house and they see her looking out into the creek with binoculars. Suddenly, behind her, three shadowy figures emerge. Eddie's brother and friends came through; their plan worked! Eddie hears rustling behind him and the friends turn to see three more mud monsters! Eddie's brother apologizes for being late.
The group turns back towards the tree house and sees dozens of mud creatures emerging from the ground, all advancing on Courtney and the tree house. They scream and yell until she notices, and all of them make a mad dash run out of the forest, escaping the mud creatures. The next day at school, Courtney is given proof that she was right, monsters do exist. Eddie and his friends are still bitter about not being able to scare Courtney, and they would love to come up with another way to scare her. But the only problem is that they are too scared to try anything else.
Plot from back cover:
IT'S GONNA BE A SCREAM! (Or) THEY'VE GOT THE DIRT ON YOU...
Courtney is a total show-off. She thinks she's so brave, and she's always making Eddie and his friends look like wimps. Nothing can scare Courtney! Or so she says... Eddie's decided he's had enough. He's going to scare Courtney once and for all. He'll lure her down to Muddy Creek. Because he knows she actually believes those silly rumors. Rumors that creepy Mud Monsters are lurking there. It's just too bad that Eddie doesn't believe those rumors, too. Because they just might be true....