In the aftermath of events that brought Thor to Earth, the universe is still in turmoil. Nine realms, once in harmony, are now out of balance. Asgard, home of the Norse gods, faces a new threat: the return of an ancient, dark force known as the Dark Elves, led by the vengeful Malekith. He seeks the Aether, a powerful, formless substance that can absorb and decimate all matter, intending to use it to plunge the universe back into darkness from which it emerged. During the convergence, a rare alignment of the realms, Jane Foster, a scientist and Thor's love interest, inadvertently absorbs the Aether, making her a target for Malekith and drawing Thor back to Earth.

Thor, against his father Odin's will, decides he must protect Jane at all costs and stop Malekith. He enlists the help of his treacherous brother, Loki, whose mastery of deception is vital for the mission. Despite the deep-seated animosity between them, they must navigate their complex brotherhood to tackle the darkness threatening Jane's life and the very fabric of the universe. In a race against time, Thor and Loki venture into enemy territory, facing betrayal and danger as they move to challenge Malekith and prevent him from using the Aether to destroy everything in his path.