When twins Theo and Alexander Sinister-Winterbottom find themselves spending their summer with their older sister Wil and their Aunt Saffronia, they’re not at all sure what to expect. It was a sudden decision. In fact, all three siblings can’t seem to remember how they got there. Well, the twins don’t anyway. Wil doesn’t pay much attention to anything other than Rodrigo, her cell phone.

But Theo and Alexander are finding the entire experience quite unusual. Aunt Saffronia doesn’t have any food and she doesn’t know how often to feed them. But she does offer to take them to the waterpark and get them a week-long pass, so they’ll have something to do for the next seven days. But when she drops them off at the side of the road, the twins don’t feel great about the idea.

But Theo is super excited about a waterpark. She loves water slides and churros, and she is ready to get started. Alexander is more of a worrier, especially concerning food preparation, so he doesn’t share her enthusiasm. But he’s willing to try out a water slide. At least, until they get to the waterpark. Fathoms of Fun is its name, but it looks like anything but fun. It’s dark and creepy, and the employees, the few ones the kids see, are dressed strangely and act even more strangely.

Theo is ready for the waterslides, and she goes on one after another after another. Alexander does give one a try, but he finds the ride harrowing and chooses to spend his time watching Theo instead. He does join her on the lazy river, even thought it’s called The River Styx, which he knows is the entrance to the underworld, but really they just drift in a big circle. The ride is even run by the one employee they like, Edgar.

Edgar tells them that the waterpark used to be better. It was still a little dark and creepy, but it was a lot more fun. But his uncle had gone missing. He’d gone into the wave pool and just disappeared. Ever since, his aunt, Mrs. Widow, had been acting strangely. Instead of cake for her birthday, she had mincemeat pie and jellied eels. And when she thinks that Alexander might be getting ideas about looking for her missing husband, she pulls him out of the lazy river and warns him to stop investigating.

That just makes the twins want to investigate more. But they’re having trouble finding any clues. It will take the three Sinister-Winterbottom siblings working together to figure out what’s going on at the waterpark and find the missing Mr. Widow.

Wretched Waterpark is the first in the Sinister Summer series. Author Kiersten White brings together fun creepiness and sibling closeness and summer vacation hijinks in this middle grade book. Fans of Lemony Snicket will throw themselves into this dark mystery, and readers who enjoy smart wordplay will enjoy in the conversations of the twins.

I really enjoyed Wretched Waterpark. I thought it was creepy but clever, and I really like the Sinister-Winterbottom kids. Some parts of the story may be a little obvious to a sophisticated reader, but it’s still a fun ride, like a waterslide you’ve already gone down several times. This one is made for summer reading at the pool or inside, when the kids are avoiding the sun. Lots of fun, with a side of scary Gothic evil and plenty of snacks.

Egalleys for Wretched Waterpark were provided by Random House Children’s (Delacorte Press) through NetGalley, with many thanks.