This tale of an ancient battle between Asgard and Olympus begins with a prologue that describes the origin of the Nine Realms and the races within, according to Norse mythology. After an account of the founding of Midgard and Asgard, we see Thor, Heimdall, and a young Sif speaking on Bifrost. Thor has heard prayers for him to intercede in a battle on Midgard.
When he arrives, Thor finds a group of Vikings battling against an enemy force that he doesn’t recognize, so he charges against them. These men are revealed to be Greeks, and they beseech their champion—Hercules—to defend them against Thor. Neither Thor nor Hercules believes the other’s claims to godhood, so they fight each other one-on-one until it is clear they are stalemated. Thor proposes that he and Hercules return to their respective homes and gather their forces to meet in battle a week later.
In Asgard, Thor tells Odin of the Olympains, and of the proposed battle between the two realms. Odin denies Thor’s request to marshal the Asgardian army, but Thor defies him and declares that he shall keep his oath. Loki, who has been spying on the conversation between Thor and Odin, sees an opportunity for mischief. He transforms himself into a fly, then buzzes off.
Meanwhile, Hercules speaks to Zeus in Olympus. Like Odin, Zeus refuses Hercules’s request to battle. However, "Thor"—Loki in disguise—bursts in and insults the Olympians, then disappears. At this, Zeus declares war, allowing Hercules to lead the army of Olympus against Asgard.
When the appointed day arrives, Thor, the Warriors Three, Balder, and Tyr lead the troops of Asgard against Hercules, Ares, Apollo, and the Olympian army. As the gods battle on, two lone figures meet on a hill overlooking the battlefield. Eventually, the Asgardians are victorious, and the Valkyries come to claim the fallen slain.
Upon returning to Asgard, Thor expects praise from Odin, but instead is chastised for sneaking into Olympus to start the battle in the first place. Thor leaves angry, imagining how his time as king will come sooner rather than later, and sets out to visit the lands he has gained through his victory.
When Thor and his companions reach Athens, they are not recognized as gods by the Greek people, but are simply looked upon as barbarians. Enraged, Thor raises Mjolnir to call down a storm, but finds that his powers do not work there. Thor hastily returns to Asgard and confronts Odin, thinking that Odin removed his powers. Odin, however, reveals the truth: the gods only exist because of the mortals who worship them—and that gods cannot conquer more lands on Earth. Because of this, Odin met with Zeus during the battle and together they agreed to create an image showing both the Asgardian and Olympian forces that they had been victorious, so each side would learn the lesson that they hold no dominion over lands on Earth where they are not worshipped.
Thor angrily strides out of Odin’s presence without a word, but is then met by Karnilla. Karnilla shows Thor a vision of the future. She foresees that eventually all people will know of Thor because of tales spread across the Earth by Vikings, and then reveals Thor’s future companions: The Avengers! Thor then admits to himself that he his still young and has much to learn, but reflects that he has no doubt of his future greatness because he is Thor, the Mighty!