Ever since he fell off the Longfellow Bridge into the Charles River and died, Magnus Chase has had a thing against falling from great heights into water. So, given the choice between repeatedly jumping from the yardarm of Old Ironsides into Boston Harbor and hanging out in his comfy room in Hotel Valhalla? Well, three guesses which he’d go for.
Unfortunately, he’s stuck with option one. The high-dive training—instruction courtesy of his cousin Annabeth’s boyfriend, Percy Jackson—is necessary if he’s going to survive his upcoming overseas voyage.

His destination is Naglfar, the Ship of Nails, also known as the Ship of the Dead. Naglfar is a nightmare vessel. As big as a battleship, it’s manned by giants, monsters, and zombie warriors called draugr, and constructed completely out of the fingernails and toenails of dead people. If that weren’t horrifying enough, Loki, the silver-tongued trickster god who recently escaped his poison-soaked prison, is the ship’s captain.

If Naglfar sets sail, it will signal the beginning of Ragnarok, the Day of Doom when the giants destroy the gods in a Nine Worlds‑ending battle. Since Magnus and his einherjar friends in Valhalla will perish that day, he’d prefer Naglfar to stay right where it is. So when the call comes for him to depart, he answers.

Samirah, Alex, Hearthstone, Blitzen, Halfborn, Mallory, and T.J. are on board for the voyage, too. Jack, his talking disco sword, hangs around his neck in pendant form, ready to be drawn at a moment’s notice. If all goes well, they will sail Magnus’s magic boat safely across the Atlantic, defeat Loki, and return in triumph to battle and die in Valhalla for centuries to come.

Unfortunately, not all goes well. . . .