In Shadows of Magic — Alison Prince

Mandy McKinney lives the charmed life. She is beautiful, athletic, popular, dating the hottest jock in school, and certainly doesn't have any time for her loser twin sister. But Mandy also has a secret. When the truth is unveiled, her world is twisted upside down, and her very life is at stake. Mandy's twin sister, Brianna, has never had any success in the dating department. When Brianna finally meets the guy of her dreams, it turns out that he has secrets of his own. Dangerous secrets. Just her luck. The twins are about to be swept away into a world of beauty and power beyond their wildest imaginations where nothing is what is seems, danger is lurking in the shadows, and their only chance of survival is finding themselves, and each other, once again.