The Wicked Waterpark of Wyoming is the 38th book in the American Chillers series being published in 2013. The author is Johnathon Rand. The illustrator for the cover is Dwayne Harris and the cover layout and design is by Sue Harring.
The main characters are Madison Armstrong and the side character is Griffin Claremont. Other characters are Sam Armstrong, his parents, waterpark employees, and dinosaurs.
The story begins when Sam shows Madison a brochure for a waterpark called WonderSplash opening in Casper, Wyoming which is two hours away from where they live in Cheyenne, Wyoming. Madison almost throws the brochure away, but the phone rings and she leaves it on the table. While talking on the phone with her friend (who is going on about her new cat), Madison and Sam's dad finds the brochure sitting on the table.
A month later, they are driving up to the WonderSplash hotel. The waterpark spooks Madison because it looks like a giant octopus that is waiting for its next meal.
In the hotel, the Armstrongs get a suite that is on the top floor. Madison claims that she has never been in a hotel this big before. Her dad asks her to run out into the hall and fill a bucket up with ice. She does this chore and at the Ice/Vending machine, a boy pulls her down to the ground.
The boy's name is Griffin Claremont and he explains that he was trying to get back at his sister for scaring him and said he thought that Madison was his sister.
Griffin and Madison talk for a while and the conversation ends with Maddie asking, "Maybe I'll see you around the park?" Griffin then says, "Yeah. Maybe. See you later."
Madison fills the bucket up with ice and gets back into her room. The next day, her parents go out to look at their old house and see how much Casper has changed. Sam stays in the room playing video games while Madison sets off exploring the park and all of its trails, pool, and playground.
Madison runs into Griffin in the lobby and he tells her that the hotel is giving free tours of WonderSplash. They don't hesitate. Madison and Griffin get into a van shuttle and when it moves, the tire blows and the kids are forced to walk to the waterpark.
Once they are there, a man tells them that they have to wait for the next group of 25 people. He tells them he'll be right back, and after that Griffin says he has to use the bathroom. He walks down the hall and opens a door. Then Madison hears him screaming that fades away. She rushes to his help and forces open the door. After that, Madison immidiately falls into a pool of water.
The same thing happened to Griffin. They swim to the side and get out of the pool. The room is dark but they find a light switch and turn it on. Madison and Griffin find themselves in a dome-shaped room. The pool is very, very deep and on the other side of it are six dark tunnels.
They decide to go down one of them, but hear footsteps. Griffin assumes it's a park employee that can help them but Madison doesn't think so because the footsteps sound like someone dragging themself. Madison and Griffin hide in another tunnel. When the creature comes out of the tunnel, it looks like a half-lizard/half-frog that stands like man, but taller.
The mutant creature jumps into the pool and Madison and Griffin come out of their hiding spot. That's when the creature erupts from the water and pulls them under. The creature's grip is very tight and they can't break free. The water is very deep and at the bottom of the pool is sand, rocks and seaweed. The creature swims to the side for a while and into a cave. He sends Madison and Griffin up to the surface, then goes back down into the water.
Madison and Griffin are now in a jungle. They swim out of the pond and onto the sand. Not too long later, they are attacked by a pterodactyl. It dives at them, they swoop out of the way, and then it goes back into the air. The kids learn that they need to defend themselves while looking for a way out of the strange world.
Madison gets a large rock and Griffin uses a long stick. They walk for a while but hide because a creature is nearing. After it passes by, Madison is attacked by the pterodactyl. It lifts her up very high and flies to a large mountain. This mountain is very odd. It is a wall that goes around and has a flat top. The mountain looks exactly like Devil's Tower.
The large dinosaur birds swoops toward a cave that is in the mountain. The dinosaur birds leaves Madison in the cave and flies off. Later, Madison sees Griffin floating up toward the cave. He explains to her that he found gum that looks like a berry and is grown on trees that allows him to fly. He gives one to Madison and they fly off of the mountain.
After that, they search for more gum and decide to go on top of the mountain to see if they can see a way out. On top of the mountain are two caves. Suddenly, the dinosaur bird comes back. Madison and Griffin hide in a cave but there is a titanoboa in it. They are nearly attacked but make it out of the cave.
Madison and Griffin see a man-made pipe that leads to the waterpark. They climb into the pipe and it takes them back but up to bars, a dead end. In the grate, they see a man in a pool room. Water splashes down the pipe but it stopped by a clear window. That means they are in a pool.
The crazy-looking man helps them out of the pipe and explains to them that the mysterious world was discovered by scientists two year earlier and that they built a waterpark over it to keep it secret. The door they entered was suppose to be locked and because they knew about the weird and wicked world below the wondersplash waterpark in wyoming, they weren't allowed to leave ever.
Madison tells him that would be illegal and suggest that they tell the weird author who wears those googly glasses to write about the incident, because if he did, everyone would know but wouldn't believe it. When Madison returns home, her parents are back and her brother is still playing video games.
A while later, back at school, Madison's teacher tells the class about something strange that happened to his nephew in Alabama. Then the story continues onto the next book, Angry Army Ants Ambush Alabama.