Review to follow.

Okay, I had serious problems with the relationships in this book, particularly around the Evil Pirate Everyone Loves Even He Is Male Toxicity Personified. We are given precisely no reasons whatsoever to like, let alone love or be loyal or go our of our way to help this scumbag, yet everybody falls over themselves out of devotion to a romanticised version of him that does not exist on the page. It's creepy and horrible. And his death makes no sense. First of all, there must have been a way of gtting the loot into the cave without dying, so there must, ipso facto, also be a way of getting it out because sealing your loot up in a cave where it can't be recovered without dying seems like a poor way to invest the wealth you have accrued through murder and robbery. So this is terrible, and all the worse because the central protagonist, a young girl devoted to the scientific study of sea-life is bloody brilliant, and I kept waiting for her increasing loyalty to her unpleasant kidnapper to turn out to be some sort of Stockholm Syndrome, or a pure survival mechanism, but no. It isn't even as if the guy redeems himself in any recognisable fashion - he's a violent narcissist obsessed with the woman who rejected him for his violent narcissism so he tries to make it up to her, or lay a massive guilt-trip on her, by dying, stupidly, after kidnapping and terrorising her grieving niece.