Now alone in a detention cell, Thor is visited by Loki. His brother tells him that their father has died, killed while vulnerable in his sleep. Loki goes on to admit that he was always jealous their father favored Thor. He confesses that he still feels threatened by his brother even though Odin is dead and Thor is stranded and powerless. Loki knows that Sif and the warriors three have left Asgard for Earth. He is now forced to take extreme and regrettable measures to ensure Thor and his friends never return to Asgard. Helpless rage overwhelms Thor as Loki vanishes from the room.
In Asgard, Loki strides into Odin’s vast armory where the all-father stored his ultimate weapon. A metal suit of armor stands alone, named simply the Destroyer.
As always, Heimdall stands vigil in the rainbow bridge transport chamber when he suddenly spies a lone, threatening figure making it’s way down the bridge toward him. The Destroyer’s heavy foot steps echo inside Heimdall’s transport chamber as the valiant guardian stands ready with his sword to challenge the giant metal monstrosity.
The warriors three walk up to the SHIELD compound and make short work of the security force remaining at the site to guard the hammer. They quickly find Thor in his cell and free him. Thor warns that Loki has probably done something that threatens everyone in the area. He insists they immediately go to the nearby town and warn Jane and the other residents of the impending danger.
Coulsen and his team arrive at ground zero of the funnel-cloud weather anomalies. Shortly after their arrival, a new storm kicks up in the skies above them. The powerful swirling winds funnel down to earth and hit the ground like a missile strike. When the cloud dissipates and the dust clears, the armored Destroyer steps forward and attacks, devastating the helpless SHIELD team.
Thor and his friends warn Jane of the impending danger. The distant funnel cloud signaling the Destroyer’s arrival was seen by everyone in town. The warriors from Asgard begin the evacuation of the town’s residents.
Thor and his friends scramble to get the last residents off to safety when the Destroyer finally arrives at the outskirts of the small town. Jane and the warriors look on as Thor, without his powers or hammer, bravely steps forward to confront the beast. Aware that Loki has to be piloting the beast, Thor tries to reason with his brother. He apologizes for all of the things that caused Loki to be resentful after becoming king of Asgard. Once Thor completes his entreaty, the Destroyer, under Loki’s control, attacks. Thor is quickly knocked unconscious by the beast’s attack. The Destroyer moves in to finish Thor off but the warriors three quickly attack from all angles. Jane and Sif rush over to Thor’s side and help him to his feet. Sif pleads with him to try once more to retrieve his hammer. Thor initially refuses to abandon his friends in a fight, but Jane reminds him of all the good he has done today, and the bravery he displayed by standing before the Destroyer to reason with Loki. HE must surely be worthy in his father’s eyes now. Sif stresses that their only chance for survival rests with a fully powered god of thunder. Reluctanly, Thor accepts their argument and races off with Jane back to the SHIELD compound.
Sif joins the warriors three in battle against the Destroyer’s unstoppable onslaught. Although they battle bravely, the four are unable to stop Odin’s ultimate weapon. The Destroyer eventually incapacitates all four warriors and moves in for the kill when the sky suddenly grows dark. A mighty bolt of lightning flashes down from the clouds above striking the Destroyer and knocking it backward. Thor soars down landing in the abandoned street with his full armor and power, ready to challenge the Destroyer. The iron monster attacks and this battle is far more devastating than the earlier fight. Thor unleashes the full power of his hammer, summoning gale force winds and striking the Destroyer with devastating blasts of energy. Vehicles are tossed about like toys and entire blocks of buildings are demolished during their conflict. Ultimately however, the Destroyer is again victorious. The monster lifts the fallen thunder god by his cape and raises him to eye level. The two are face-to-face as the Destroyer’s visor plates open. He prepares to finish Thor with his powerful destroyer beam when the thunder god gestures with his hand. His hammer flies to his waiting grip and Thor instantly lifts the weapon above his head and slams it down hard over the Destroyers open visor just as the energy blast is unleashed. The trapped energy from the Destroyers open face visor explodes. Thor is sent flying backward and the Destroyer drops to both knees. Smoke billows from the open neck of the monster as the armor falls limp and inanimate to the street.
Thor rises and regroups with his friends to ensure everyone is okay. He approaches Jane and they share a final kiss before he and the others are to return to Asgard to confront Loki. Thor promises Jane that he will return to her. He turns and leaves with his warrior friends for their final battle in Asgard to depose Loki.
In Asgard, having lost control of the defeated warrior armor, Loki and the frost king begin to panic. The frost king is increasingly frustrated that Loki has been stalling about killing the still slumbering Odin. Realizing the opportunity to kill Odin grows short, the frost king makes his way to the sleeping monarach. Loki grabs Odin’s spear and uses it to attack the unsuspecting frost king just as he is about to kill Odin. Loki confesses to the dying frost king that he essentially did everything as a way to earn Odin's respect. He never intended to kill his father, he just wanted Thor out of the way so he could become the favored son for once. With the frost king dead, Loki turns his thoughts to the return of Thor. He grips the mighty Odin spear with both hands and prepares for his brother’s arrival.
In the transport chamber, Thor arrives but is surprised to find that Sif and the other three warriors aren’t with him. Heimdall lies on the floor unconcous. Suddenly Thor is ambushed by Loki who has been waiting for him. Loki states that even though it is impossible for either of them to kill the other, he will ensure Thor suffers by going to Earth himself and killing the new mortal woman he has developed feelings for. Upon hearing this, Thor uses his hammer to destroy the central console, the only way for Loki, or anyone, to get to Earth. The energies released by the destroyed console wreak havoc within the domed chamber. Loki races out of the building and Thor chases after him, resuming their battle outside on the bridge. The unchecked energies inside the great chamber cause a massive implosion. A swirling singularity erupts in its place and begins draw in everything in the vicinity. Thor and Loki both desparately grab onto the edge of the bridge, struggling to avoid being consumed by the swirling wormhole. Suddenly, Odin appears, finally awaken from his slumber, and reaches out to his two sons. Loki tells Odin that he "did this all for him" and Odin replies that he didn't want peace "like this." Loki realizes he failed his father once again and lets go of the bridge, allowing himself to fall into the collapsing wormhole just as it exhausts itself and disappears.
Back in the Asgard palace, all is well. We see Thor on what remains of the rainbow bridge asking the Gatekeeper what Jane Foster is doing back on Earth. Heimdall replies "She is searching for you."
Final shot of the film is of Natalie Portman, Kat Dennings and Stellan Skarsgård inside a room working on their science equipment.