Magnus Chase Tome 3 - Grand Format

Loki the trickster god is free from his chains. He's put together a crew of giants and zombies to sail Naglfar, the Ship of the Dead, in a battle against the Norse gods. If he succeeds, the final battle of Ragnarok will extinguish all the worlds. With help from Percy Jackson and my cousin Annabeth, and with friends by my side, I have to sail across the oceans to reach Naglfar before Midsummer's Day.
The only problems are the angry sea gods, hostile giants and evil fire-breathing dragon in the way. But even if we survive the journey I'll need more than just Jack, my talking sword, to beat Loki. I must find a magical elixir so deadly that it will either make me powerful enough to defeat Loki and put him back in chains for good ... or destroy me entirely.