Dead Beat (Dresden Files Book 7) by Jim Butcher
A vampire contacts Dresden and asks him to get a necromancer’s book for her. If he doesn’t, she’ll go public with some photos she has of action from previous books that show Lieutenant Murphy committing homicide (admittedly on some supernaturals who were trying to kill her, but the photos will still wreck her career and maybe send her to prison).
His deadline is Halloween: he has three days to get the book. Meanwhile, several powerful necromancers have turned up in Chicago, all seeking the book. Each wants to use it for a “ritual of ascension” to make himself or herself a god.
Dresden has some friends to help him: Billy the werewolf, and Thomas his vampire half-brother who rooms with him (a situation that makes most new acquaintances assume that the impossibly good-looking Thomas must be his gay lover).
Much comic mayhem results, and Dresden gets a new friend: the smart, though somewhat fearful, polka-loving medical examiner Butters. His interactions with Dresden are hilarious.