Iron Druid Chronicles, book 3: HammeredKevin Hearne2011

Thor, the Norse god of thunder, is worse than a blowhard and a bully—he’s ruined countless lives and killed scores of innocents. After centuries, Viking vampire Leif Helgarson is ready to get his vengeance, and he’s asked his friend Atticus O’Sullivan, the last of the Druids, to help take down this Norse nightmare.

One survival strategy has worked for Atticus for more than two thousand years: stay away from the guy with the lightning bolts. Plus things are heating up in his home base of Tempe, Arizona. There’s a vampire turf war brewing, and Russian demon hunters who call themselves the Hammers of God are running rampant. Despite multiple warnings and portents of dire consequences, Atticus and Leif journey to the Norse plane of Asgard, where they team up with a werewolf, a sorcerer, and an army of frost giants for an epic showdown against vicious Valkyries, angry Norse gods, and the hammer-wielding Thunder Thug himself.