At school that day, Courtney is happy which Justin notices during the day. At the locker, she says that all she needed was a good nights rest, until she opened her locker, and a spring loaded plush spider shot at her. This scares her as Priscilla makes fun of her, making Courtney realize this is her handy work. Courtney gives Oogie to Justin as she goes to get even despite Justin and Oogie saying that's not a good idea. Courtney then shoves Justin into a locker and tells him that she doesn't consider him, Alex, Elsa, and Oogie friends and to leave her alone. She then storms off to take care of Priscilla. Justin asks Oogie if something happen leading Oogie to tell him about the mask. Justin decides to go see Stranger after school to get some answers.
In the girl's changing room, Priscilla hears about missing football players being at attacked by a monster girl from her friends. They told her Leon told the cops everything that happened since Josh was drunk, but the cops didn't believe him thinking he took drugs before it happened. Priscilla doesn't believe it as she starts getting dressed, just as her friends scream and fear and disappear. Priscilla becomes really scared and then comes face to face with Courtney possessed by the mask again. She demands and scares the camcorder and an apology out of Priscilla and then trapped Priscilla in a cocoon of flesh, smashed the camcorder, and made off with the cocoon without anyone knowing about.
After school, Justin arrives at the store and mentally prepares himself in case Stranger says no to helping him or allowing Justin to help him. He and Oogie go to Library Wing to find no one there. He sees the spot where the Book of Goosebumps used to be as he thinks about the scientific part of is still having a hard time accepting the situation he's in, despite all he has seen so far. Elsa and Alex walks in as Stranger suddenly appears out of nowhere. Justin says he wants to help with the monster quest by being the group's tech guy for weapons and anything else useful. Alex despite thinking he has nothing to do with this, says he photography skills give him a good eye, good at hiding, and never gives up till the truth comes out. Elsa is not sure it's a good idea to bring them in, but Stranger says yes due to his age catching up with him. Justin and Oogie then tell Stranger about what is happening to Courtney which makes Stranger reveal what the mask really is. The Mask is one of many created by a mask maker he, Elsa, and Stine met in their travels who used monster hides to make human faces. Over time though they turned into monster faces making the maker call them the Unloved Ones due to no one wanting them. Overtime they became sentient, evil, and gained symbiotic features allowing them to possess and later take over their hosts until the wearer becomes a monster in mind, body, and soul. The one Courtney has is the last one and the most powerful in existence since Stranger, Elsa, and Stine destroyed the others and trapped that one in the book. He tells the group that the only chance for Courtney to take the mask off is for a symbol of love to make Courtney accept the faults she has while wearing it to take it off herself. The group starts getting ready to go and find Courtney before it's too late.
Meanwhile, in an abandoned church, the Haunted Mask makes more possessed masks for the missing jocks along with Priscilla and her friends in order to make them monsters for it to control and attack the town with. Courtney tries to break free of it's control feeling ashamed if her dad saw her life this, but is unable to as the mask takes control of her again. The new masks attach themselves to the cocooned students as they transform into monsters for the mask to take revenge of the world that shunned it.