Moonshine by Rob Thurman

Moonshine:
After saving the world from his fiendish father's side of the family, Cal Leandros and his stalwart half-brother Niko have settled down with new digs and a new gig-bodyguard and detective work. And in New York City, where preternatural beings stalk the streets just like normal folk, business is good. Their latest case has them going undercover for the Kin-the werewolf Mafia. A low-level Kin boss thinks a rival is setting him up for a fall, and wants proof. The place to start is the back room of Moonshine-a gambling club for non-humans. Cal thinks it's a simple in-and-out job. But Cal is very, very wrong.

Cal and Niko are being set up themselves-and the people behind it have a bite much worse than their bark...

Moonshine is the second book in the Cal Leandros series by Rob Thurman, and through Cal's narration we are taken into a part of New York's werewolf underground as Cal and his brother, Niko, go undercover for the Kin - the werewolf Mafia. Betrayed by who they believed to be their inside contact when he kidnaps the beloved local psychic, Georgina. The wary brothers form a loose alliance with a werewolf named Flay (a.k.a. Snowball by Cal), and the unlikely team of human, half-Auphe, Vampire, a Puck and werewolf are pulled deeper into the betrayers deception. During this action-packed book, Cal battles with his distrust of himself, seeing himself as a monster and the reason for Georgina's kidnapping. The prospects for her rescue become all the more bleaker when Niko is defeated and taken during battle (a very hard feat as you'd know if you read the first book, Nightlife) to be used as a blood sacrifice. Niko has been the only constant in Cal's life as they struggle to survive from the things that go bump in the night, and for Niko and now Georgina, Cal would willingly sacrifice his own life to gain their freedom. A much different side of Cal is revealed in Moonshine, his sarcasm and snarkiness are still very much apparent (he just wouldn't be Cal with out them) but deeper emotions are also revealed for those who surround him as he battles for those he loves.