At school, the students get ready to go home for a week-long vacation, Casper sees Mosshead crying and asks him what is wrong, Mosshead tells him that he has to stay at school for the whole week since his kinfolk is going out to scare at a new condo development and they think he is too young to go with them and can't stay at the swamp neither. Casper then invites him to stay with him at his uncles' house and he accepts. As they head for the manor, Mantha and Ra try to warn Casper about Mosshead but he insists that if they are nice to Mosshead, he'll be nice back before Mosshead asks him to drag his hugh crate all the way to the manor.
Mosshead turns out to be an horrible houseguest after he leaves moss everywhere, eats Fatso's food, sneezes on the dinner, sleeps on Casper's bed without his permission and snores loudly while his pet toad Ricardo croaks and don't let Casper sleep, which forces him to sleep in the living room. The next day, Casper wakes up to see his uncles scolding at him, the trio demands Mosshead goes away, Casper refuses to kick him out since he is their guest so the Trio leaves.
Later, Casper makes Mosshead play Hide-and-Shriek so he hides somewhere and Casper can go see "Killer Mutant Pig Bunnies 2" with Jimmy but he spots Mosshead running around the city and tries to distract him whle he goes to meet Jimmy but when he reaches the Bradley Residence Mosshead finds him and scares Jimmy until he makes him crash against garbage cans. When Casper helps Jimmy to his feet Mosshead realizes they are friends and intends on telling everyone at school, causing Casper to snap and chew Mosshead out for being an "obnoxious jerk" and that if Mosshead tells on him, he won't help him ever again. Mosshead apologizes and runs off to start cleaning the manor. Casper returns home and he and Mosshead start cleaning the house until the Trio shows up with Stinky's "Super Sucker 4000" and his newest invention the "Bottomless Box".
The next week, Casper and Mosshead aboard the ship to return to school, Thatch sees Mosshead with the Bottomless Box and, thinking it was a present, snatches it from him and opens it, leading to him getting covered on moss and other random objects.