The Indigo Spell, by Richelle Mead

Alchemist Sydney Sage is still at a prep school in Palm Springs helping protect a Moroi princess from assassination. But she has a lot of other things on her mind. She is under threat from a predatory witch and must quickly develop her illicit magical powers to defend herself. She has to track down the rogue Alchemist Marcus and find out if the Alchemists really are working with the Warriors against the Moroi. And then there is Adrian, for whom she is developing totally inappropriate feelings and who wants more from Sydney than she is allowed to give. The poor girl is pulled every which way and must figure out her priorities and what she really wants out of life, rather than just doing what she is told. Will Sydney abandon her upbringing, her training and her duty to join the renegade Alchemists? It may be the safest option. The Bloodlines story is a bit in stasis in this novel while Sydney does some growing up. There is a feeling that future novels really need to move on from the high school setting, which has become somewhat irrelevant, to take the action forward. The love story has a nice momentum, but Sydney’s growth has now taken her well beyond the convenient school cover and it needs to change.