Magnus Chase and the Hammer of Thor Boo by Rick Riordan

Thors 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 isnt just lost it has fallen into enemy hands. If Magnus Chase and his friends cant retrieve the hammer quickly the mortal worlds will be defenseless against an onslaught of giants. Ragnarok will begin. The Nine Worlds will burn. Unfortunately the only person who can broker a deal for the hammers return is the gods worst enemy Loki an Paperback softback