Jillian and Jackson are twin sister and brother. Their neighbors, Artie and Nina, are also twins and new to town, but they really don't like them. All four end up in the same movie theater. Artie spills buttery popcorn all over Jackson's new sweater, and Nina just acts really annoying. The manager comes over and tosses them all out, and Nina and Artie's parents accidentally spray the other twins with water while driving through a puddle.
They find a fortune telling machine on the street and try their luck. All they get is a card that says Welcome to HorrorLand on the front.
When they get up the next day, Jillian realizes that something changed. She can read the thoughts of everyone around her, and Jackson can move things with his mind. Things get even more intense at school. Jackson freezes the clock in class to make the teacher think she has more time and run out before giving them a quiz. Jillian can read the thoughts of others, and after reading Nina's mind a few times, the other girl freaks out.
They sneak out of the house and into the nearby park to try out their powers. They don't have super strength and they can't fly, but they do see a weird person watching them. He has the face of an extremely old man and the body of a kid. He introduces himself as Finney and tells them that their powers alerted The Brain Institute about them. Though they aren't in the mood to take off with some weird guy, he transports them to The Institute.
There, they meet Inspector Cranium. He tells them that he works for the Thought Police and tracks brain waves to find those with super powers. The kids hide their powers from him by thinking about the other twins. Though he says that he never makes a mistake, he agrees to let them go home and gives them his card. The card lets them know that they didn't fool him and that he'll continue watching them.
When they try to tell their parents what happened and what's going on, they lose their memories temporarily. It turns out that The Institute is a little more powerful than they thought. They also go over to the other twins' house. Jillian keeps reading Nina's mind again, and Jackson plays a Wii game with Artie. Ugh, I hate seeing modern references! They fight, and Jackson ends up freezing both twins with his mind. It isn't until their parents come home that they get free.
It's now time for the twins' birthday. After a lame party where Nina ruins Jillian's shirt and Artie whines a lot, Inspector Cranium shows up. He freaks out about how they can't escape him, but it turns out that he's really talking about Nina and Artie. They do a bunch of crap that ends with him floating around on the ceiling. Nina reveals that they were born with super powers and spent their whole lives on the run. Artie then tells them that he has power over time. He uses his powers to turn the inspector into a baby and makes him disappear down the street.
Jillian and Jackson go back to their house the next day to talk with them more about the whole Institute and Thought Police thing. They find the house dark and empty with no sign that anyone ever lived there. While wandering around town and trying to decide what to do next, they find the fortune telling machine. After putting in some money, they get another card that welcomes them to HorrorLand.
HorrorLand Story Time!
Jackson and Jillian arrive in HorrorLand as Very Special Guests, but on the way to the Doom Slide, they come across the inspector. He chases them to the ride, and they choose a slide at random. The inspector yells out that Maniac will get him for letting them go.
They get away, only to have two detectives/guards stop them. The guards make them go to a magic show, where the magician only seems interested in doing them as much harm and pain as possible. Jillian reads one boy, Robby's, mind and learns that he created the magician. He pretends to die, she sides with him, the magician goes crazy and runs away screaming about Maniac.
Matt and some of the kids from the other boys bring them up to date on everything that happened so far. He still wants to find the cafe where the original two girls escaped. Matt takes them to the wall that blocks the cafe, pulls out his key card, and tries to open the wall again. Jackson then uses his super powers to actually rip apart the wall.
The whole group runs inside and finds the mirrors in the cafe, which will let them escape. Some of the kids get through, but the rest get stopped by some Horrors. By the time they get back to the mirrors, they're solid again and they can't get through. They run to a lake, hop on some canoes, and take off, but it turns out that the canoes have no bottoms. After nearly drowning, they all swim back to shore.
Two kids, Lizzy and Luke Morris, show up. Jillian realizes that she saw them earlier watching them from behind a building. They claim that they want to help and that the kids need to stay in HorrorLand. One of the others asks Jillian to read their minds and see what's going on. Jillian quickly discovers that they're lying to them...