Jim Butcher's The Dresden Files: Fool Moon #6

Harry's barely survived an attack by the legendary loup-garou - a werewolf of unimaginable power and ferocity - but the worst is not over yet. A building full of Chicago police officers has been utterly savaged, and one of the beast's victims is an officer he's worked with countless times in the past. With the deaths of friends and strangers alike weighing on his conscience, and a multitude of enemies hell-bent on his destruction, Harry comes face to face with the one person who might be able to unravel the mysteries tearing apart his life: Himself...