There were aspects of this book that were interesting, mainly the first half of the book, but somewhere along the way I felt like the story sort of crashed and burned.
Firstly, the concept of Marin. Marin is an underworld city that is actually an old spaceship. This idea could have had merit if it was established, but instead the characters just think that it's very convenient that everything, and I mean absolutely EVERYTHING, has been provided for them. Nobody questions this. Nobody wonders why an alien race with a massive ship was close enough to earth to be able to crash land. Nobody even wonders how the clearly advanced civilsation become extinct when they could have easily taken over the world with their advanced technology. Everyone is just so accepting of this and it is extremely frustrating.
Then comes the characters. The central characters aren't so bad, but the people of Marin are the worst. They rebel against their king for his brother who all the people know murdered his own father, the previous king, and who has mounting evidence against him that all but proves he has been cutting up women to turn them into mermaids. And do you know why the citizens want to follow him? Not because he has proven himself, or because he has shown leadership skills that exceeds his brother's, but because he got his girlfriend pregnant first and all the people of Marin view this as a sign. His brother wasn't having sex with his girlfriend so of course she wouldn't be pregnant. So the people of Marin forget about all the current king did for his people to keep them safe, and align themselves with his insane brother because he knocked up his girlfriend.
Later on, the main character, Miranda, makes a speech about storming the castle with a bunch of civilians with no battle plan whatsoever, no weapons, no exit strategy, or no idea about what their actually going to do once they go inside the castle walls. And the hundred or so people she's gathered are just like, "You'll make a great queen, Miranda," seemingly overlooking that just days prior everyone was pledging their allegiance to the crazy king.
I feel like a lot could have been done with this story, but it all, as I said before, crashed and burned with plot that makes no sense half the time and expects the reader to just follow along as it goes around in circles, and a civilisation of idiots who feed people to sharks as capital punishment and are so easily manipulated it has gone past the point of believable. Though the ending does offer a hook that makes me a little curious, I can't stop thinking about how much I disliked the world of Marin and its people. I don't think I'm going to bother with the next one.