I really wanted to go for this one. It really could have worked.
I honestly didn’t even mind the BIG TWIST, which, you know, when your narrator has traumatic brain damage, it’s almost like, “Of course,” when ~*~ things aren’t what they seem ~*~.
I just felt very disconnected, very removed from the proceedings. Which may be a direct function of the narrator/protagonist feeling that way herself, due to her memory loss and bouts of illness keeping her out of the loop, both in understanding of the past and in participation of the present. But typically I get immediately attached to a lot of stories that dangle the carrot and tell me very little and entice me with the promise of piecing together the puzzle as I go. That never really quite happened here.
I’m wary of explaining my apathy away by suggesting this is a book of rich people’s problems, therefore unimportant, therefore I don’t care. For one thing, it’s just not true; I’ve been entertained many a time by the trials and tribulations of the wealthy — The Real Housewives of New Jersey was amazing, for like two seasons.

^ Classic.
For another thing, I’m not sure if that’s relevant to the actual problems with this book. YA in particular is exceptional in dealing with nuances of family and exploring the different ways that young people grow out of their experiences, particularly when those experiences are informed by the type of people their parents are. Cadence is privileged, and acts it, and is called out for it. But she is also growing up with some bad examples of how to treat your loved ones, and receiving bad messages of what kind of treatment to expect in return. Most of the romantic relationships she’s witnessed have ended in divorce, and the one couple that is still together is, in so many words, being slowly poisoned by Cadence’s racist grandfather, who won’t let them get married (yes, the aunt in the relationship has plenty of responsibility here too.)
So, I get Cadence as a sympathetic protagonist, despite her privilege. She doesn’t have a lot of role models in her life, and, long story short, her family basically drove her to where she ended up. Being surrounded by that much callousness and narcissism is a poor situation for anyone, regardless of how much money they have. I think in the process of writing all of that out, though, I may have come around to the problem that I had, which was that, while none of the above is technically a spoiler, it’s still not really made clear until the end. The book really just goes so quickly from zero — Cadence doesn’t remember anything, and sits dreamily on the island having really mild and meaningless interactions with everyone there, not provoking her memories to return at all — to sixty: I SUDDENLY DO REMEMBER HOW MY FAMILY FIGHTS ALL THE TIME AND NOW I REMEMBER EVERYTHING ELSE.
So, I don’t know. The non-linearity and twist could have totally worked, if some of the pacing was a little more even, maybe. There just wasn’t enough of a slow build of clues; everything just came rushing back right at the end.
And just because I can’t help but get really specific for a second (following paragraph is SPOILERS, avoid as necessary):
Do the adults know that the kids intentionally burned down the house, and, in particular that it was Cadence’s idea? Like, the only way I can see all of them being so nonchalant about not wanting an arson investigation is if they know that the kids did it. But, at the same time, I also do not see how the aunts and grandfather would be so pleasant with Cadence when she returns to the island, if they knew. The book made such a point of showing how spiteful and selfish the adults are, that I do not believe they would also not project their grief at her, the survivor. Or, you know, they’re so selfish that they’re not that sad their kids are dead, I guess.
END SPOILER
So, obviously, I am not among the many that fell in love with this book. I am surprised I didn’t react more strongly to it in either direction, because it seems formed to generate a reaction. Usually I would give a book like this three stars, but I’m being a little less generous with my stars this year because of going back and seeing how I have given the same rating to books I actually like, but had problems I chose to overlook, versus books that I just kind of didn’t care about. I think the former still gets point for evoking emotion, whereas the latter, I won’t even mentally revisit.