Magnus Chase, a once-homeless teen, is a resident of the Hotel Valhalla and one of Odin's chosen warriors. As the son of Frey, the god of summer, fertility, and health, Magnus isn't naturally inclined to fighting. But he has strong and steadfast friends, including Hearthstone the elf, Blitzen the dwarf, and Samirah the Valkyrie, and together they have achieved brave deeds, such as defeating Fenris Wolf and battling giants for Thor's hammer, Mjolnir. Now Magnus faces his most dangerous trial yet. His cousin, Annabeth, recruits her boyfriend, Percy Jackson, to give Magnus some pointers, but will his training be enough? Loki is free from his chains. He's readying Naglfar, the Ship of the Dead, complete with a host of giants and zombies, to sail against the Asgardian gods and begin the final battle of Ragnarok. It's up to Magnus and his friends to stop him, but to do so they will have to sail across the oceans of Midgard, Jotunheim, and Niflheim in a desperate race to reach Naglfar before it's ready to sail. Along the way, they will face angry sea gods, hostile giants, and an evil fire-breathing dragon. But Magnus's biggest challenge will be facing his own inner demons. Does he have what it takes to outwit the wily trickster god?

"Magnus Chase, you nearly started Ragnarok. What are you going to do next?" It's been six weeks since Magnus and his friends returned from defeating Fenris Wolf and the fire giants. Magnus has adjusted to life at the Hotel Valhalla—as much as a once-homeless and previously alive kid can. As a son of Frey, the god of summer, fertility, and health, Magnus doesn't exactly fit in with the rest of Odin's chosen warriors, but he has a few good peeps among his hallmates on floor nineteen, and he's been dutifully training for Ragnarok along with everyone else. His days have settled into a new kind of normal. But Magnus should have known there's no such thing as normal in the Nine Worlds. His friends Hearthstone and Blitzen have disappeared. A new hallmate is creating chaos. According to a very nervous goat, a certain object belonging to Thor is still missing, and the thunder god's enemies will stop at nothing to gain control of it. Time to summon Jack, the Sword of Summer, and take action. Too bad the only action Jack seems to be interested in is dates with other magical weapons. . . .

"Magnus Chase, you nearly started Ragnarok. What are you going to do next?" It's been six weeks since Magnus and his friends returned from defeating Fenris Wolf and the fire giants. Magnus has adjusted to life at the Hotel Valhalla—as much as a once-homeless and previously alive kid can. As a son of Frey, the god of summer, fertility, and health, Magnus doesn't exactly fit in with the rest of Odin's chosen warriors, but he has a few good peeps among his hallmates on floor nineteen, and he's been dutifully training for Ragnarok along with everyone else. His days have settled into a new kind of normal. But Magnus should have known there's no such thing as normal in the Nine Worlds. His friends Hearthstone and Blitzen have disappeared. A new hallmate is creating chaos. According to a very nervous goat, a certain object belonging to Thor is still missing, and the thunder god's enemies will stop at nothing to gain control of it. Time to summon Jack, the Sword of Summer, and take action. Too bad the only action Jack seems to be interested in is dates with other magical weapons. . . .