Magnus Chase, a sixteen-year-old homeless boy living on the streets of Boston, is woken under a bridge by his friend Blitzen, who warns him that people are handing out flyers with his name and picture. Magnus spots his cousin Annabeth Chase and her father Uncle Frederick searching for him in the Public Garden.
Magnus overhears them mention his Uncle Randolph, who has apparently just told them Magnus's mother is dead and Magnus is missing. Remembering his mother's warnings to stay away from Randolph, Magnus decides to break into Randolph's Back Bay mansion to look for answers rather than approach his relatives directly.
Magnus breaks into Randolph Chase's brownstone mansion and helps himself to food. Exploring the library, he finds Viking artefacts, old maps, and a leather pouch of runestones. From the window he spots Hearthstone standing by the Leif Erikson statue, signing at him to get out.
Before Magnus can leave, Randolph appears in the doorway. The imposing, white-bearded man tells Magnus they don't have much time and that, since Magnus has turned sixteen, people will be coming to kill him.
Chapter 3: Don't Accept Rides from Strange Relatives
Randolph reveals he knows about the wolves that killed Magnus's mother and claims Magnus's father is a Norse god. He says Magnus has a birthright - a weapon lost in a shipwreck near the Longfellow Bridge - and that finding it is the only way to survive. Despite his mother's warnings, Magnus agrees to go with Randolph after hearing the building shake from distant explosions.
Randolph drives recklessly toward the Longfellow Bridge while lecturing Magnus about Norse exploration of North America. He explains that his life's work has been studying how the Norse sailed to Boston, and that a millennium-old shipwreck near the bridge contains Magnus's birthright. He confesses he lost his own wife and daughters at sea searching for it, and finally tells Magnus his father is a Norse god.
On the Longfellow Bridge, Magnus stretches his hand over the river and magically pulls a corroded sword from the water. Before he can examine it, Surt, a terrifying fire giant in a dark suit, erupts onto the bridge in a column of flame. He demands the sword, threatening to incinerate the bridge and everyone on it.
Chapter 6: Make Way for Ducklings, or They Will Smack You Upside the Head
Blitzen and Hearthstone charge in to help Magnus, armed with toy weapons from a nearby shop - a MAKE WAY FOR DUCKLINGS sign and a plastic Cupid's bow. They attack Surt but are quickly overpowered. Magnus orders Blitz to get Randolph to safety and turns to face the fire lord alone.
Magnus walks through Surt's wall of flame, discovering his immunity to extreme temperatures. The corroded sword transforms into a gleaming Viking blade in his hand and fights almost on its own, slashing Surt's leg and cutting off his nose. But Surt hurls a ball of molten asphalt into Magnus's gut. Dying, Magnus grapples Surt and they both plummet off the bridge into the Charles River. Above, Magnus glimpses a girl on a spectral horse diving toward him.
Chapter 8: Mind the Gap, and Also the Hairy Guy with the Axe.
Magnus dies and dreams of hiking with his mother at the Blue Hills. He then finds himself in Randolph's library, where a scarred man in a Red Sox jersey - Loki - greets him cryptically and tells him not to trust appearances. Magnus is pulled through grey fog by the armoured girl on the spectral horse, who carried his soul from the bridge. He wakes in a courtyard before an opulent town house with wolf-head doorknockers and is greeted by a surly doorman named Hunding, who informs him he is dead and leads him inside to register.
Magnus enters the Hotel Valhalla, a massive hunting lodge with warriors in bathrobes, armed waitresses, and a daily schedule of combat to the death. The manager Helgi checks him in and explains this is where he will stay until Ragnarok. Hunding the bellhop shows him to his room, mentioning that his Valkyrie will come for him before dinner.
Magnus explores his enormous suite, which features an open-air atrium, a wall of his favourite books, and a framed photo of him and his mother at Mount Washington - a picture that burned in the fire. Overwhelmed by finally having a safe, comfortable place, he breaks down. He flips a sofa across the room with surprising strength, discovering his einherji upgrade.
Chapter 11: Pleased to Meet You. I Will Now Crush Your Windpipe
Samirah al-Abbas arrives at Magnus's room - the girl who chose his soul on the bridge. She reveals she is his Valkyrie, a living teenager who attends King Academy in Dorchester and does calculus homework between reaping souls. When Magnus says he is no hero and asks about his mother, Sam pins him against the wall, warning him never to say that - her career is on the line. She introduces herself properly and escorts him to dinner.
Magnus meets his floor nineteen hallmates: Thomas Jefferson Jr., a Civil War soldier; Mallory Keen, a fiery Irish girl; the half-troll X; and the berserker Halfborn Gunderson. Sam explains that Valhalla groups warriors by the age they died and that Valkyries choose the einherjar. She reveals she lives in Dorchester with her grandparents. They enter the enormous Feast Hall of the Slain, with its central tree, magical goat, and thousands of warriors.
At the newcomers' table, Magnus eats magical feast beast and drinks mead brewed from goat's milk. Gunilla, captain of the Valkyries and daughter of Thor, confronts Sam, accusing her of bringing a spy. Sam warns Magnus that Gunilla is powerful. The feast begins with presentations of new einherjar.
Chapter 14: Four Million Channels and There's Still Nothing On Except Valkyrie Vision
Gunilla has fitted the Valkyries with cameras, and new einherjar are judged by video of their deaths. Six impressive newcomers are presented - warriors who saved lives and died heroically. A vala reads runes to determine each warrior's parentage. Magnus watches nervously, knowing his turn is coming last.
The Valkyrie Vision footage of Magnus's death has been edited to make him look incompetent - Blitz hitting Surt with a ducklings sign, Hearth's squeaky arrow hitting Magnus's butt. The thanes debate whether Magnus died worthy. Sam defends him but is undermined by Gunilla's doctored video. Lord Ottar calls Sam "daughter of Loki," revealing her parentage.
Three enormous white Norns rise from the lake beneath the World Tree and pronounce Magnus's fate: he is the son of Frey, "Harbinger of the Wolf," and "wrongly chosen, wrongly slain." They prophesy that in nine days the Sword of Summer will unbind a beast. The thanes accept Magnus grudgingly but expel Sam from the Valkyries for her poor judgment. Before vanishing, Sam urgently tells Magnus he must find the sword.
Magnus spends a restless night pondering the Norns' prophecy and his father Frey, a god of spring, summer, and abundance. He discovers his body has been upgraded with new muscle. A note from T.J. invites him to breakfast in the floor nineteen lounge.
At breakfast, Magnus learns more about his hallmates: T.J. died at Fort Wagner as a son of Tyr; Halfborn has been in Valhalla twelve hundred years since the Viking invasion of East Anglia; Mallory died disarming a car bomb; and the half-troll X was brought by Sam after fighting dogfighters in Chicago. They tell Magnus that leaving Valhalla is possible but dangerous, as einherjar lose their immortality outside.
Magnus's first day on the battlefield of Valhalla is brutal. His hallmates fight together against thousands of einherjar who target him as the new arrival. Halfborn goes berserk, T.J. charges a hill singing battle hymns, and Mallory fights ferociously. When surrounded and disarmed, Magnus instinctively unleashes a blast of alf seidr that strips weapons from a hundred warriors, before being killed by a bone steel axe.
Chapter 20: Come to the Dark Side. We Have Pop-Tarts.
Magnus dreams of Loki lounging on Odin's throne Hlidskjalf, eating Pop-Tarts. Loki explains how Frey once sat on this throne, saw what he most desired, and gave away his sword because of it. Loki warns that Surt will use the sword to free his son, the Wolf, in eight days. Then Surt appears in a nightmare vision, threatening to burn Magnus and his friends. Magnus wakes to find Gunilla at his door, offering a tour of the hotel.