Siblings Billy and Sheena Deep are spending their summer vacation on the Caribbean island of Ilandra with their uncle named Dr. Deep. A zoo crew wants Dr. Deep to find and trap a mermaid that has been reported in the area. While swimming, Billy is almost killed by a hammerhead shark but is saved by the mermaid whom Dr. Deep traps in a large glass tank.
After his experiences in Monster Blood, Evan has a series of nightmares relating to animals. His friend Andy has kept some monster blood and the two decide to bury it in the woods. Despite their doing so, the monster blood ends up getting dug up and fed to a hamster who becomes gigantic and starts destroying things.
Gary Lutz is afraid of bees and his next-door neighbor, Mr. Andretti, is a beekeeper. Gary finds an advertisement online for a company that will allow him to switch bodies with another customer. When Gary agrees to switch bodies with a muscular skateboarder named Dirk, the company mixes things up and instead puts Gary's mind into the body of a bee.
The Morris family, and their friend Clay out on a day trip, attempt to find Zoo Gardens amusement park, but fail as they forgot the map, so instead they stumble upon HorrorLand. The family car inexplicably explodes in the parking lot and the monstrous ticket-taker promises it will be 'taken care of'. When the various attractions the family explores at the park all threaten to kill them, they attempt to escape HorrorLand and save their lives.
Eddie is constantly being outdone by his classmate Courtney who demonstrates that she is far braver than he is. Eddie plays a series of practical jokes on Courtney that all backfire and serve to further demonstrate her superior bravery. In his final effort to scare Courtney, Eddie and his friends dress up like mud monsters, but before they can sneak up on Courtney, real mud monsters sneak up on them and scare them away.
