Twilight Watch by Sergei Lukyanenko

The third book in Sergei Lukyanenko's dark and thrilling Night Watch series—a visionary blend of urban fantasY and riveting thriller, set in contemporary Moscow

Night Watch and Day Watch revealed the "Others," an ancient race of supernatural beings—magicians, shape-shifters, vampires, and healers—who live among us and swear allegiance to either the Dark or the Light. For a millennium, these opponents have coexisted in an uneasy truce, guarding each other and tottering on the brink of war.

In Twilight Watch, the Others face their greatest threat yet. An ancient book of spells with the power to turn ordinary humans into Others has fallen into the wrong hands, threatening to destroy the precarious balance between the forces of Darkness and Light. Now the Night Watch and the Day Watch must cooperate to stop the culprit. Anton, the hero from Night Watch, is back, but when the renegade Other turns out to be closer to home than he expected, the race to prevent global war becomes more urgent than ever. And as Anton gets closer to discovering the true nature of the Others, he begins to question how much of a difference there truly is between the Dark and the Light.