Between the cover and the promise of cults, I was very drawn to this book. And I think the drawing me in was the point. If you're looking to read about a cult, you're only barelyyyyyy going to get that here. To the extent that the characters in the book are constantly saying "this is kind of a cult, huh? ish? a little?"
I was also drawn in by the anecdote at the start of the book, it's a creepy little story that got me excited for who this "cult leader" Clive character was. But the rest of this book is slow and navel-gazing. Each sentence felt overwrought, and yet important backstory is missing. We're told that the MC has been super close to some of the characters, Clive in particular, but until the events of the book, there's really no indication of what drew them to each other or why they cared about each other. The main character's relationship to the experiment didn't make sense to me, she's freaked out, she's excited, she... stops showering and almost no one mentions it? Sadly, by the end, I felt nothing, for her relationship or for the people she knew or reconnected with along the way. 
I got this book from NetGalley and the publisher (thank you!) in return for an honest review. I wish I could say I enjoyed it, but I'd skip it and try another book from MCD, whose books have always worked for me in the past!