Beautiful Darkness is frustrating a lot of the time to read, since the narrator/protagonist is so often frustrated, and it 'infects', for lack of a better word, the reader. Ethan Wate, said narrator, is an interesting character in that he badly wants to understand the situation(s) and do the right thing, but the people around him consistently marginalize him and treat him.......well not badly, this isn't Harry Potter after all, but rather dismissively. Their attitude becomes "oh fine, if you must know I'll explain it to you", and I can't decide whether that's a good story device or not. On the one hand, it creats sympathy for Ethan himself, and gives him a nobility that a lot of teenagers in these kinds of novels lack. On the other, it can create a situation where the authors can make up rules as they go along. 
 The story is essentially a road story, becoming more a more a staple in YA fiction, along with the requisite 'lovers torn apart by events', which always has been a staple. Ethan and his Caster girlfriend Lena are having difficulties that Ethan, as I previously said, really doesn't understand. As in he doesn't get why there are problems at all. He's not obtuse, Lena just won't explain them to him. She disappears with the mysterious hybrid John Breed, whose motives don't seem especially good, and Ethan feels compelled to chase after her and protect her, even though he's not sure that he can. And that's the story really, Ethan searching for Lena. 
 New characters include the aforementioned John Breed, as well as Liv, assistant to librarian Marian, in both her responsibilities. From moment one Liv is set up as the Mortal counterpart to John Breed, and she and Ethan do have chemistry. Back from Beautiful Creatures are: Link, still dumb but totally steadfast, and he has an arc in the story as well surprisingly; Ridley, the Siren who's nothing but trouble; Lena's various relatives, who range from complete evil to benignly crazy-ish; Amma, Ethan's......I'm not really sure what she is, his family retainer or something. She's less of a presence in this book, thankfully. 
 But the real reason to read the novel is Ethan/Lena. Lena goes from mysterious in the first book to selfish in this one, and it's not a transition that favors her. A bit more/better of an explanation for her taking off like she did would have been nice. But Ethan is what kept me reading, he's a good everyman kind of character, and I could relate to him.