The Unbelievable FIB 2 - Over the Underworld

"It's started. Ragnarok has started. It's the end of the world." It's been a year since friends ABE and Pru joined Mister Fox's Fantasy Investigation Bureau to save their hometown from an invasion of Viking gods and giants. Life has been incredibly ordinary ever since. Then the Norse Allfather, Odin, appears with terrible news: Baldur, his favorite son, has been murdered-the first step in a fated chain of events that leads to Ragnarok.
In the second book in the Unbelievable FIB series, ABE and Pru must outrun trolls, explore Asgard and the Viking underworld, and try to outsmart the Queen of the Dead herself to save the world-and survive seventh grade.