The Avengers: Earth's Mightiest Heroes!

Synopsis

In their various realms, the Avengers prepare for their final confrontation with Loki. At the great Forge of the Dwarves, Tony Stark and the Dwarf King Eitri work on a new suit of Iron Man armor for Stark. Ant-Man and the Wasp travel with the Valkyries. Black Panther and Hawkeye fly aboard a magical ship, while Hulk is accompanied by the Warriors Three. Meanwhile, on Asgard, Loki plans the execution of several heroes of Asgard, including the Avenger Thor, the final step in claiming sole rule over Asgard. The places are set for an epic final battle.

The Frost Giants and Loki loyalists stand guard at the edge of the Bifröst bridge. Hulk and the Warriors Three are the first to arrive and battle the Giants, soon joined by the Valkyries along with Ant-Man and the Wasp. Soon overwhelmed, the heroes are rescued by the flying ship that carries Hawkeye, Black Panther and the elf Faradei. After everyone is informed of Loki's plans to conquer the Nine Realms, the gathered heroes plan to storm the Asgardian palace.

In Nifleheim, the Realm of the Dead, Captain America is offered a heroes rest and reward by Hela, the ruler of the dead. He rejects her offer, however, saying that his work among the living wasn't yet done battling Baron Zemo. Hela reveals that Zemo was merely a pawn in Loki's larger scheme. Learning that Thor is in trouble, Captain America demands that he be returned to battle. Before Hela can release him from her realm, however, she strikes a bargain: if he is killed in the battle with Loki, Captain America's spirit belongs to her.

While Loki attempts to tap into the power of the World Tree, Yggdrasil, he learns that the heroes of both Earth and Asgard are pushing a final attack against his defenses. Declaring that he will kill the Avengers before executing Thor, Loki conjures a giant hunting trumpet and blows into it, summoning a huge monster, Hoarfen the Ice Wolf.

The Avengers are initially overwhelmed by Hoarfen, only for Captain America to appear and formulate a workable strategy against the enormous wolf. With an organized attack, the Avengers are able to herd Hoarfen in such a way that it crashes into Loki's palace, both knocking the creature out and giving them access to the God of Mischief.

The heroes demand Loki's surrender, but he attacks them using the Odinforce, the most primary magic in all of Asgard. Loki quickly overwhelms the Avengers, even destroying Captain America's Vibranium shield. Just as he is about to defeat the Earth's mightiest heroes, Iron Man arrives in his new armor, built of uru, the same metal Thor's hammer is made of.

Iron Man, the Hulk and Wasp begin to fight Loki, while some of the other Avengers attempt to free Thor from the magical shackles Loki has caught him in. Once freed, Thor tells Ant-Man, Hawkeye and Black Panther that Loki was able to draw from the Odinforce by corrupting the Yggdrasil. If they can break his connection to the World Tree, he can be defeated. Meanwhile, Thor joins the battle against Loki.

Black Panther reveals that Wakandan scientists, after studying Mjolnir, were able to create technology capable of seeing magical energies, and can confirm that Yggdrasil is the focal point of most of Asgard's magic. While examining the tree, two ravens attack the Avengers with deafening screams. Growing his helmet to better stand the force of the raven's screams, Ant-Man shrinks down and examines the roots of Yggdrasil more closely.

Meanwhile, Loki gets the upper hand on the Avengers again until Thor rejoins the battle, having reclaimed his hammer. Outside the palace, Loki starts to lose his control of the powerful Odinforce, threatening each of the Nine Realms with ultimate destruction. Thor warns Loki that he could begin Ragnarok, but Loki pays him no heed as the Odinforce begins to wash over the entirety of all the Realms.

Within the palace, Ant-Man grows to giant size and uproots Yggdrasil. After it has been removed from its plot, a new World Tree grows in the place of the old, and the Odinforce returns to Odin. Rejuvenated, Odin awakens from the Odinsleep. Confronting Loki, Odin says that his actions are not mere trickery, but actual evil. Loki shows no regret before Odin uses the Odinforce to cause him to disappear, claiming he has been banished to somewhere far worse than the Island of Silence.

In the Palace of Asgard, Thor is congratulated by Odin for saving the Nine Realms from Loki's destruction. Thor, however, gives credit to his comrades in arms, the mortal Avengers. Odin tells the Avengers that they have earned the respect and thanks of the Asgardians. Elsewhere, Loki awaken to find himself the captive of the World Serpent.

Back at their mansion, the Avengers retire to their personal quarters. Once inside his room, Captain America examines his broken shield and considers the deal he made with Hela. His personal reflection is interrupted when another Captain America steps out of the shadows. Before Cap can respond, he is shot with an alien weapon and falls to the floor. The second Captain America states that "the infiltration has begun," before transforming into a Skrull.

Production Notes

The title for this episode comes from the traditional preamble to most Avengers comics: "And there came a day, a day unlike any other, when Earth's mightiest heroes and heroines found themselves united against a common threat." This is also where the show gets its title.

This is the finale of Season 1. Show runners Joshua Fine and Christopher Yost have confirmed that the show has been ordered for at least two full seasons, with a second season of 26 episodes to start in October of 2011.

The end of this episode teases an adaptation of the Secret Invasion storyline from the mainline Marvel comics. This was previous teased at the end of the episode Widow's Sting, as well as the disappearance of Nick Fury from SHIELD since the episode Hail Hydra!.