Rebel Angels by Libba Bray

Gemma is looking forward to spending time with her friends in London over Christmas--but her troubled visions of three girls dressed in white are intensifying. Something very bad has happened to those girls--and only the enchanted realms can give Gemma the answers she needs. Evil threatens a happy reunion with Felicity, Ann, and Pippa, and soon Kartik appears with a warning, telling Gemma that she must find the Temple and restore order before the realms are lost. But if Gemma lives out her destiny, her actions will bring her face to face with Circe, her dead mother's closest friend--and her own mortal enemy.