Carly Beth is chilling at home when she hears something calling her to the basement. When she gets there, she realizes that it's the mask from the regular Goosebumps book. It encourages her to wear it, and the next thing we know, it's the next day and she's riding the bus with her friend Sabrina. She tells her all about how it took all her willpower to not put the mask on. Just then, she looks down and sees a vicious snake wrapped around her neck. Nah, it's just a pet snake someone brought to school.
She and Sabrina volunteer or work, not sure which, at this former farm that now functions as a petting zoo, a museum, and apparently a daycare center. They arrive and see this girl named Laura working. Even though she's only 12, she was left in charge of like six kids. The kids all run around outside and start racing towards this mysterious building on the edge of the property. Laura flips out and calls them all back.
Laura then decides to tell them the story of the haunted stable. A farmhand sneaked inside one night to scare the head stable guy. Something went wrong, and the people on the farm heard the horses actually screaming. When they got there, they found all the horses dead and the stable boy crushed underneath them. Laura explains that it was all due to a weird and mysterious mask that only shows up at Halloween and how people say the stable is now haunted.
Cary Beth thinks it's weird because (a) it might be the same mask and (b) she swore that she heard horses there. Sabrina then comes up with this great idea to do a report on the stable for school. She drags her back, and Carly Beth for some reason brings along carrots. They hear horses and she freaks out, which leads Sabrina to explain that it was just a trick that she planned with some of their classmates. The only problem is that the other kids never showed up and the carrots go missing. When they go to leave, Carly Beth sees a young boy standing in the shadows on the roof of the stables.
She later goes back to check out the stable for herself and sees a cute boy there. He introduces himself as Clark and first says he lives there before correcting himself and saying that his family lives nearby. They talk a little until she brings up the ghost story. He laughs it off and says that he doesn't believe in ghosts and has never seen anything paranormal there. When she goes to leave though, she hears the horses again.
Cut to Carly Beth randomly stumbling across the store where she bought the mask. In the last book, she tried to find it again and discovered that it disappeared. The shop owner refuses to take back the mask. He tells her that she didn't actually defeat it like she thought and that there's someone out there in the world who once owned the mask that is coming back for it.
Carly Beth goes back to the farm for some special Halloween party with the kids. She ends up finding a book about the history of the farm while on an errand and sees a picture of Clark in the book listed as one of the original stable workers. Clark shows up to party, Carly Beth flips out, and asks Sabrina to keep all the kids away from him. She then confronts him about what she found, he admits that it was him, and then he laughs it off and says it was his grandfather.
The kids then start screaming because their homemade masks stick to their faces. Laura rushes in and reveals that she was the daughter of the farm's first owner and that it was her who wore the mask and scared the stable boy. She demands the mask, but Carly Beth doesn't know what happened to it. Sabrina admits that she stole it from her house and randomly buried it by the stable.
Carly Beth runs and gets it, and decides that she must fight evil with evil. Laura causes Clark to fly through the air and smack his head right as she puts on the mark. The two have some massive fight that ends with all the ghostly horses come out of nowhere and basically trample Laura. Carly Beth can't really get the mask off until the horses come to her. Laura tells her, as the horses nuzzle her, that when she brought the carrots, they viewed it as her being nice to them and no one has been nice to them since they died. The horses disappear and the mask comes off.
When she drops the mask on the ground, it turns to her and lets her know that it will be back to see her next Halloween...
Carly Beth received an invitation to HorrorLand in the mail and decided to take Sabrina. Not long after arriving, they hear two boys, Matt and Billy, talking about some missing girls. Being extremely nosy, they ask what's going on. Billy explains that his sister Sheena went missing and that they lost two other girls too. Matt shows them his magic mirror, which shows the missing girls. Carly Beth really just wants to go have fun, but Sabrina convinced her that they need to help.
While at a magic show, the magician does a disappearing act, and Sheena somehow pops up. When they go backstage, they find a name tag belonging to Byron, the Horror who agreed to help them. Sheena tells them that she was with the two missing girls, accidentally stumbled through a door, and wound up back in the park. After her announcement, they break into two groups.
Sabrina and Carly Beth wind up in a mask shop, where she thinks that she sees the haunted mask. After trying on a few masks, they wander into the back room and see masks that look just like the missing girls. The masks warn them that they're next. Carly Beth is freaked out enough that she wants to leave the park and go back to the hotel. After passing a sign about werewolf territory, they see a bunch of guys with wolf-like faces. While running away in fear, they discover that they're locked inside the park and that someone is after them.
*Some kid in their class just got her nose pierced. Am I the only one who thinks 12 is way too young for that?
*Carly Beth snaps at her brother that he's worse than most five year olds, which is his age. He snaps back that she's worse than most four year olds, which I thought was pretty funny.
*She also complains because her mom and dad like playing video games and she thinks they're too old. She should come by my house! Between the three of us living here, we have two XBOX 360 consoles, a PS3, a Sega Genesis, Nintendo Wii, a Kinect, a PS2, and an original Turbo Grafix 16.