The Prophecy of Shadows (Elementals, #1)

Witches are real. They're descendants of the Greek gods.

Nicole Cassidy is a witch descended from the Greek gods... but she doesn't know it until she moves to a new town and discovers a dangerous world of magic and monsters that she never knew existed.

When the Olympian Comet shoots through the sky for the first time in three thousand years, Nicole and four others -- including mysterious bad-boy Blake -- are gifted with elemental powers. But the comet has another effect -- it opens the portal to another dimension that has imprisoned the Titans for centuries. After an ancient monster escapes, it's up to Nicole and the others to follow a cryptic prophecy in time to save the town... and possibly the world.