Fallen, by Lauren Kate

Book one in the Fallen Trilogy. Book three got great reviews, so I figured I should start from the beginning. This is a pretty typical YA novel, similar in outline to the dreaded Twilight books, but "starring" angels instead of vampires, et al. Lucinda transfers to a reform school after she is involved in a tragic and deadly event at her former boarding school. Sword and Cross is not a typical prep/reform school: untidy, ugly, weird-but-not-criminal kids, and apparently lots of very hot guys, one of whom is quite charming and attentive, another of which seems to hate her on sight.

Of course, she is drawn more to the latter boy, who ends up being more attentive than he seems while Mr. Charming turns out to be a...well, demon.

War breaks out, her best friend turns out to be mortal after all, and the librarian, while not at all stereotypical, is definitely a villain.

Book Two awaits!!