*free copy from NetGalley in exchange for a review*

I'm not sure how to start this review, except by saying that I was so damn engaged by this book I ended up hunched over my tablet late at night with my hood up, because I'm scared of giant sea creatures but couldn't stop reading.

This book was really something. I am obssessed by the idea of a thirty-three minute water slide!? Like, the sheer SCOPE of that is insane. Imagining that suspended above the London skyline is something else, and I think the constant movement of the characters through the flume was what kept the book from dragging. All of the imagery was incredible, and the idea of being stuck in this flume in the middle of an electric storm? Terrifying. The book is split into three segments with three different parts of the flume - the Core being the most interesting and also the scariest for me - and the world-building and backstory to it is amazing.

Grammatically, this book was perfect. No complaints at all, the writing flowed and our three main characters jumped off the page. I really enjoyed Flo and Yam as a pair of friends for the main character, the former being a techy girl who likes numbers and fixing things, and the latter being something of a hippy boy who goes with the flow (pun not intended). Shanks, the protagonist, was interesting as a narrator, and I found all of his flashbacks and the way his backstory mystery unfolds - as well as the story of Mr Poppity, the explorer who created the flume in the first place - satisfying (even if a smidge predictable).

Me finding it satisfying does not, however, mean that this book was not really, really weird. I love weird books, and I'm not going to spoil the ending, but it was just straight-up bizarre. If you had asked me how the book would end, I would have guessed about a thousand other endings before the one I read. It feels like a bit of a fever dream, or perhaps a very odd simulation. Also, I have some questions regarding Flo and Yam and whether or not they were supposed to be reincarnations of certain people, or whether they just shared similarities to help Shanks jog his memory. Either way, I enjoyed their company all the way down the flume, and I'd say it's still less traumatising for a child than Jacqueline Wilson's The Cat Mummy, so would probably recommend it to upper-primary school.

Tl;dr: An inventive fever dream. 4.5 stars.