Iron Druid Chronicles, book 1: HoundedKevin Hearne2011

Atticus O'Sullivan, last of the Druids, lives peacefully in Arizona, running an occult bookshop and shape-shifting in his spare time to hunt with his Irish wolfhound. His neighbors and customers think that this handsome, tattooed Irish dude is about twenty-one years old - when in actuality, he's twenty-one centuries old. Not to mention: He draws his power from the earth, possesses a sharp wit, and wields an even sharper magical sword known as Fragarach, the Answerer.

Unfortunately, a very angry Celtic god wants that sword, and he's hounded Atticus for centuries. Now the determined deity has tracked him down, and Atticus will need all his power - plus the help of a seductive goddess of death, his vampire and werewolf team of attorneys, a sexy bartender possessed by a Hindu witch, and some good old-fashioned luck of the Irish - to kick some Celtic arse and deliver himself from evil.