Lady Sif and The Dark World

In the distant past, a cosmic event known as the Convergence occurs, opening portals between the Nine Realms. A sinister race called the Dark Elves attempts to use the Convergence as a way of unleashing the Aether, a **** of destruction with the capability of destroying the entire galaxy. The exact origin of the Aether is unknown, but it is known that it is one of six powerful objects that predate the universe itself. The leader of the Dark Elves, Malekith, nearly succeeds in using the Aether to cause the instantaneous destruction of the Nine Realms under the misguided belief that he can recreate them in his own image. He is opposed by Bor, the then-king of Asgard and the father of Odin, who uses the Bifrost to rip the Aether from Malekith's grasp just as he attempted to enact his plan, robbing the Dark Elves of their most potent weapon. Driven back to their homeworld, Svartalfheim, it becomes apparent that the Dark Elves cannot defeat the Asgardians and are all but wiped out in the battle. While the Asgardians, unable to destroy the Aether, seal it away in a place it can never be found, Malekith, his lieutenant Algrim, and various survivors manage to escape into suspended animation, vowing to one day return and finish their plan.

5,000 years later, after the Chitauri Invasion, Thor is brought before Odin in shackles. Odin gives Thor a life-sentence in prison for his crimes against humanity. One year later, in Vanaheim, home of the Vanir, Loki, Sif, alongside warriors Fandral, Volstagg, and Hogun, fights against the Marauders, a ragtag group of invaders that have been systematically terrorizing the Nine Realms for the past two years. The Asgardians win the battle, and while Hogun remains on Vanaheim to help his people rebuild, Loki and his friends return to Asgard via the Bifrost Bridge, which was repaired by the power of the Tesseract. A party is held in celebration for Loki's victory, but he leaves quickly. He visits Heimdall daily, asking each time how his sleeper agent Jane Foster is making advances in Earth. Odin clearly does not approve of Loki's affections for Foster as she will be dead long before him.

Back on Earth, Jane Foster (under mind control of SHIELD) is in London, to investigate readings of unknown nature obeying orders of SHIELD. She is contacted by Darcy Lewis, who explains that Foster's scientific equipment has been picking up strange signals, signals that have not been detected since the events that took place in New Mexico two years prior. They find that a number of portals have opened, linking the Earth to several different worlds and altering the laws of physics, causing gravity to shift without warning. While Lewis continue to play around with the portals, Foster is swallowed up by one of them and transported to an unknown planet. She finds herself in a dark chasm, where a strange vault is located. Upon touching the vault, a red substance, the Aether, emerges from it and infests her body. Malekith note her and use an ancient spell to take control of her mind and order her infiltratw in Asgard. Passing out, Foster is teleported back to Earth, waking up five hours later. She walks outside where Lewis have been waiting. The police had been called there by Lewis and consequently attempt to arrest the two for trespassing on private property; a policeman tries to touch Foster, but the Aether forces him away. Prior to that, Sif suddenly arrives, sent by Loki to investigate Foster's well-being, as Heimdall lost sight of her after she disappeared. Sif takes her to Asgard to investigate the nature of the Aether.

Once there, Heimdall greets them, but Jane Foster is quickly taken to the healing chambers so that they can learn what's wrong with her. They find the Aether in her body but they don't know what it is. A physician called Eir tries to remove the Aether from Foster but fails. Odin, angered that a human has entered Asgard, orders for her to be taken back to Earth, but when a guard touches her wrist, the Aether reacts defensively just as it did with the police. Odin, recognizing the Aether, tells Foster of its many possible origins using the Book of Yggdrasil, and how the Dark Elves nearly used it to destroy the realms. While Odin works to find a way to remove the Aether without killing Foster, Frigga befriends and protects her. Frigga has secretly been attempting to convey her disappointment to Thor regarding his actions, but he has rebuffed her every time.

Meanwhile, alerted by Foster, Malekith prepare his attack to Asgard. Under Malekith's orders, Algrim allows himself to be captured by the Asgardians while in disguise as a Marauder and, using vile technology, turns himself into Kurse, a superpowered warrior that the Dark Elves used frequently in their war against the Asgardians. He frees all the prisoners except Thor and they start a prison riot, distracting the Asgardians so that Malekith can lead his squadron of ships into Asgard with little opposition. A battle takes place, during which the palace is breached and heavily damaged. Frigga, having suspected the diversion, lures Malekith into a duel by creating a holographic replica of Foster. Frigga nearly succeeds in besting Malekith, but Foster intervenes and mortally wounds her with Aether when Malekith command her. During rhe fights, Sif disfigures Malekith's face with a bolt of lightning, forcing the Dark Elves to retreat. Frigga then dies from her injury.

A funeral is later held for the dead Asgardians and Frigga, and a grief-stricken Odin has Jane Foster confined. Loki knows that Malekith will return for Foster, but Odin, blinded by hate and grief, refuses to release her and intends to destroy Malekith through whatever it takes. So, Lokicomes up with a plan to move her, even though he would be committing treason. With Heimdall distracting Odin from them, Sif has Thor freed from his cell, as Loki knows of secret portals that could transport Foster to another world, drawing Malekith away from Asgard. With help from Fandral, and Volstagg, Loki, Sif, Foster, and Thor hijack a downed Dark Elf ship and make their way out of Asgard and to a hidden portal that teleports them to Svartalfheim. As they make their escape, however, Foster's body is slowly being infested by the Aether, draining her of life.

The group lands in the wastelands of Svartalfheim and by then, Foster's body has completely channeled the Aether, enhancing her perceptions but weakening her physically and put her completely under control of Malekith. Melekith senses the Aether's transfer and confronts the group on Svartalfheim, and at that moment, Thor appears to betray Lokk, cutting off the hand of Sif and giving Foster to Malekith willingly. Thor tells Malekith that in return for the Aether, he wants a front row seat to watch Asgard's destruction. Malekith then proceeds to drain the Aether from Foster's body and into himself, but Thor's betrayal is revealed to be a ruse, and Sif's injury is revealed to have been nothing more than a holographic projection meant to lull Malekith into a false sense of security.

Calling for Mjølnir, Sif tries to destroy the Aether, but fails as it is indestructible. Kurse then battles Loki and Sif while Malekith and his minions leave the planet, and Kurse quickly gains the upper hand against Sif. Thor comes to Loki's aid, stabbing Kurse through the chest with the sword, but this has no effect on the Kursed, who seizes Thor and drives the sword into his own body. Thor manages to press one of Kurse's implosion bombs, however, and sets it off, destroying Kurse. Thor then apologizes to Loki for his actions, and seems to die in his arms. After mourning Thor; Loki, Sif and Foster then enter a cave, believing that they have failed in stopping Malekith. Suddenly, Foster's cell phone gains reception and they venture deeper into the cave, finding a portal. The portal teleports them safely back to London. Meanwhile, an Einherjar Guard appears in the same area where Thor died, and returns to Asgard to inform Odin of what transpired.

While Jane Foster has been in Asgard, Darcy Lewis has been fruitlessly trying to reach S.H.I.E.L.D. Darcy meet up with Loki, Sif and Foster, and Darcy tells them that she discover the people who lived in England after the previous Convergence had built certain objects to create a secret map to where the Convergence would reach its peak. The location is revealed to be Greenwich. After putting two and two together, Foster theorizes that Malekith plans to spread the Aether through the portals so that he may destroy all of the worlds at once.

They travel to Greenwich the next morning, and when they arrive, they find that a number of portals have opened up above the city, a sign that the Convergence is nearing its peak. Malekith soon arrives, and Sif engages him in battle, with both evenly matched. The fight takes them through various portals throughout the city, transporting them to different worlds. While the two are fighting, the scientists use Darcy's devices to deal with the Dark Elf soldiers, accidentally summoning a Frost Beast in the process.

Sif and Malekith are soon separated by one of the portals, and Malekith, now unopposed, unleash the Aether into the portals. Thor soon regroups with his friends and takes Darcy's devices, noting that while the Aether might be indestructible, Malekith himself is not. Using the devices, Sif impales Malekith with them, allowing Foster to teleport him back to Svartalfheim, stopping his attack. However, Malekith's damaged Ark starts to crash, and nearly crushes Sif and Foster, when Darcy uses the last of his devices to teleport it away; it ends up on Svartalfheim and lands on Malekith, killing the Dark Elf leader. The portals then close, and the ordeal is finally over.

Some time later, Loki returns to Asgard, where Odin congratulates him on his victory despite the crimes he committed to do so. Odin comments that Loki will make a wise king, but Loki responds by saying he is not ready to bear the weight of the throne. Loki leaves Asgard to reunite with Foster and Sif on Earth to prepare operations in Earth, but as he leaves, Odin is revealed to be Thor, having faked his **** and usurped Odin's throne.

Later, Fandral hand over the captured Aether to Taneleer Tivan. Tivan appears eager to take it but is curious as to why the Asgardians don't just keep it secured in their own vault. Fandral explains that the Tesseract is already on Asgard and that to keep two Infinity Stones in the same place would be unwise. As they leave, the Collector remarks "One down, five to go." Loki returns to Earth, where he reunites with Sif and Foster to planing take Earth, unaware that the Frost Beast that was teleported to Earth during the Convergence is still running rampant through London chasing a flock of birds.