The Twilight Watch - Sergei Lukyanenko - Paperback

The Night Watch, book 3 of 5, ungoing series

Walking the streets of Moscow, indistinguishable from the rest of its population, are the Others. Possessors of supernatural powers and capable of entering the Twilight, a shadowy world that exists in parallel to our own, each owes allegiance either to the Dark or the Light.

Night Watch Agent Anton Gorodetsky's holiday is abruptly shortened when an urgent call from Gesar - his boss and Night Watch head - forces him to return to work.