"Magnus and friends help the god of thunder find his missing weapon before all Muspellheim breaks loose"-- "Thor's hammer is missing again. The thunder god has a disturbing habit of misplacing his weapon--the mightiest force in the Nine Worlds. But this time the hammer isn't just lost, it has fallen into enemy hands. If Magnus Chase and his friends can't retrieve the hammer quickly, the mortal worlds will be defenseless against an onslaught of giants....

In the city of Hodorf, the Tattercoats live by a strict code. So when a boy named Otto gets caught up in the devious plottings of a former disgraced Tattercoat, Nim takes it upon herself to come to Otto's rescue.