Night Watch by Sergei Lukyanenko
They are the "Others," an ancient race of supernatural beings—magicians, shape-shifters, vampires, and healers—who live among us. Human born, they must choose a side to swear allegiance to—the Dark or the Light—when they come of age.
For a millennium, these opponents have coexisted in an uneasy peace, enforced by defenders like the Night Watch, forces of the Light who guard against the Dark. But prophecy decrees that one supreme "Other" will arise to spark a cataclysmic war.
Anton Gorodetsky, an untested mid-level Light magician with the Night Watch, discovers a cursed young woman—an Other of tremendous potential unallied with either side—who can shift the balance of power. With the battle lines between Light and Dark drawn, the magician must move carefully, for one wrong step could mean the beginning of annihilation.