A small human named Nicky is taking out the garbage. He spots Ickis, who startles him. Nicky alerts his older brother of this monster, who thinks Nicky is crazy as he saw Ickis as a "bunny rabbit". Nicky is now angered, but continues with his chores.
The Gromble announces to all of his monster students that it is Halloween and that monsters are banned from walking out of the dump. He tells them that he has three punishments for anyone who disobeys him: "bad", "really bad", and "you don't want to know". Ickis, Krumm, and Oblina are disappointed, as they were planning on escaping to the human world. After school ends and they are in their room, Ickis doesn't want to disobey the Gromble so Oblina and Krumm convince him.
Nicky, the human whom Ickis scared the night before, dresses up as Ickis for Halloween, which makes Nicky's brother Jake and his friends laughing at him thinking Nicky's a purple bunny rabbit. The monsters escape from the dump and see kids getting candy, all three monsters try to scare the kids, but the kids think that they're humans in costumes, not real monsters. The monsters have reached two houses and a party; after the monsters leave the party, Jake (Nicky's brother) and his friends start egging and T-P-ing the neighborhood. One of Jake's friends mistake Ickis for Nicky, and Krumm and Oblina mistake Nicky for Ickis.
Nicky is taken back to the trio's dorm where they find out Ickis is Nicky in costume, and Ickis gets in Nicky's clothes to fake himself as Nicky. Nicky as Ickis is taken to Monster Academy, and Ickis goes to Nicky's school, when Nicky's teacher asks him to describe his house to the class, but instead of describing Nicky's house, Ickis describes the dump; resulting in him getting detention. After school: Nicky, Ickis, Jake, and Jake's friends go back to the house to trade Halloween candy, so Ickis suggests to flush himself down the potty. But when Jake rips off Ickis's hat, They both get into a fight; triggering Ickis's scare mode and chasing Jake's friends away.
Nicky gets home safely and the monsters are united back together. Back at the Monster Academy, the monster trio thinks they're being punished by the Gromble, are being treated like royalty. Though they did disobey him, they have to choose which punishment. Ickis asks what the third punishment, labeled "You Don't Wanna Know" is, so the door opens revealing a black screen with someone screaming.
- Before Jake pins Ickis to the floor, Ickis was in his Nicky disguise, but when Ickis is on the floor the disguise clothes disappear.
|Gregg Berger||The Gromble|
|Steven L. Hartman||Nicky|
|Susan Blu|| Mom|
|Gabrielle Boni|| Kid #2|
|E. Faye Butler|| Teacher|
|Jim Cummings|| Herb|
|Debi Derryberry|| Little Girl|
|Jarret Lennon||Kid #1|
|Aaron Michael Metchik|| Kid #3|
|Ron Taylor||Monster #2|
|Erik Von Detton|| Vic|