A Chill in the Blood — P.N. Elrod

When he was alive, Jack Fleming was a reporter with a nose for news. Now that he's dead, he's a private eye with a thirst for justice--and blood. But being a vampire with morals is no midnight stroll on the streets of post-prohibition Chicago. In the city of sin, the gangs still rule--and they're on the brink of an all-out war. Neither crooks nor cops care how much blood, innocent or otherwise, flows during the fight. But Jack does.

Caught between the local hoods and the boys from New York, Jack has to stop the battle before it starts. But how much of his remaining humanity will he have to give up to do it?