Thor (Chris Hemsworth) is imprisoned on the planet Sakaar, and must race against time to return to Asgard and stop Ragnarök, the destruction of his world, at the hands of the powerful and ruthless villain Hela (Cate Blanchett).
Thor makes it off Sakaar along with Bruce Banner and Valkyrie and returns to Asgard to confront Hela and her forces. He realizes during the battle that the only way to stop her is to destroy Asgard since her power is drawn from there. He does so, and manages to escape with the surviving Asgardians (rescued thanks to the help of Loki and Heimdall) before finally taking his place as ruler.
The movie opens with Thor learning from the fire demon Surtur that Ragnarok, or the destruction everything, will occur once the eternal flame rests on his crown. To prevent this, Thor defeats Surtur and brings his removed crown back to Asgard to prevent it from being reunited with the eternal flame in Asgard’s stronghold.
When he arrives, he discovers that Skurge is now guarding and controlling the Bifrost bridge and that Loki has been masquerading as Odin while the real Odin and Heimdall have been living in exile. With the help of Dr. Strange on earth, Thor and Loki track down Odin in Norway. Odin tells them that he is about to die, and with his death, his firstborn, a daughter named Hela, will return to wreak havoc on Asgard, and that only they can stop her.
Sure enough, no sooner does Odin vanish to Valhalla than Hela the goddess of death appears and demands that Thor and Loki kneel to her. When they refuse and fight back, Hela immediately destroys Mjolnir, leaving Thor seemingly powerless. Loki inadvertently leads her back to Asgard by calling for the Bifrost Bridge. On their way, Hela knocks both Thor and Loki into the depths of space. Upon her arrival to Asgard, she kills several guards while Skurge obediently kneels to her out of survival. She takes Skurge under her wing and continues to lay waste to Asgard, easily dispatching all that stand in her way, until she revives the army of Asgard’s dead warriors and the Fenris wolf, to further her conquest.
Thor and Loki wind up on the planet Sakar, where Thor is captured by Scrapper 142, a former Asgardian Valkyrie. Valkyrie sells Thor to the Grandmaster where he discovers that Loki has been living the sweet life as part of the Grandmaster’s entourage.
Thor is chosen to compete in the Contest of Champions, before which he is given a haircut by Stan Lee. In the arena, Thor discovers that the two-year undefeated champion is none other than Hulk. After the fight, Hulk befriends Thor, who eventually finds the Quinjet Hulk had used to fly to Sakar after the battle of Sokovia. When he plays back the video of Natasha Romanoff, Hulk transforms back into Bruce Banner for the first time in two years. Loki and Valkyrie are tasked by the Grandmaster to return Hulk and Thor to him, but the two fight, ending with Loki forcing Valkyrie to relive the battle against Hela, where all her comrades were killed. Valkyrie agrees to help Thor stop Ragnarok.
With the help of Valkyrie, Banner and Thor are able to get back to Asgard to face Hela. Banner transforms back into the Hulk while Valkyrie, and the remaining Asgard warriors fight the army of the dead. Loki arrives in a stolen ship from Sakar to protect the Asgardians while Thor faces Hela. Skurge sacrifices himself so that the ship can take off. Thor is easily no match for Hela, losing his right eyes in the fight. As Hela is about to deliver the final blow, Thor realizes that his power never came from Mjolnir, and that he is the god of thunder. Thor uses his godly ability to control thunder and lightning to hold Hela off and destroy the rest of the undead army.
Thor then tells Loki that the prophecy was never intended to prevent Ragnarok, but to cause it, as it is the only way to surely defeat Hela once and for all. Loki returns to the palace while Thor distracts Hela. Loki places the crown into the eternal flame, thereby resurrecting Surtur and beginning the annihilation of the planet of Asgard. With all of Asgard’s people safely aboard the ship, Thor, Loki, Valkyrie, Hulk, and Heimdall leave as Surtur destroys Asgard, and Hela with it.
Now wearing an eyepatch like his father before him, Thor, the new king of Asgard, commands that a course be set for Earth.
While traveling through space, the ship is blocked by a much larger ship. The ship belongs to Thanos, who knows that Loki took the Space Infinity Stone from the Asgard stronghold (the tesseract).
The Grandmaster emerges from his ship to a revolution, and confidently suggests that the people consider it a draw.
The movie begins two years after Avengers: Age of Ultron, with Thor (Chris Hemsworth), having failed in his quest to locate the Infinity Stones and having also been dumped by Jane (although he insists it was a ‘mutual dumping’) hanging above a fire pit before being brought to the presence of fire demon Surtur. Thor is told by Surtur it is his (Surtur’s) destiny to bring about Ragnarok, which is the complete destruction of Asgard. Thor learns from Surtur that Odin (Anthony Hopkins) is not on Asgard, so uses Mjolnir (his hammer) to escape and destroy Surtur, keeping his crown/skull. He returns to Asgard and sends Surtur’s skull down to the vaults but then finds Heimdall (Idris Elba) has been replaced as sentry of the Bifrost Bridge by the inept Skurge (Karl Urban) who explains that Odin accused Heimball of treachery causing Heimdall to flee.
Reaching Asgard, Thor sees a massive statue of Loki (Tom Hiddleston) as well as Odin lounging around watching a play about Loki’s ‘heroic sacrifice’ while fighting the Dark Elves. Realizing what’s happened, Thor quickly forces Loki (who usurped and disguised himself as Odin prior to the end of Thor: The Dark World) to drop his charade and demands to know what happened to Odin. It is revealed that Loki had placed Odin under a spell and dumped him in a retirement home in New York but by the time they get there it is being demolished. Before they can plan their next move, Loki is suddenly pulled through a hole and a card with an address is left behind. Heading there, Thor finds in the presence of Doctor Strange (Benedict Cumberbatch) who agrees to help him find Odin on the condition that all Asgardians leave Earth. Thor agrees, and after doing some research (during which Thor is constantly teleported around the Santum much to his displeasure) Doctor Strange finds that Odin is in Norway. He then releases Loki from his endless fall, and when Loki goes to attack an exasperated Strange unceremoniously sends them both through a portal.
They find Odin in Norway overlooking a cliff (having shaken off Loki’s spell) and he admits that he is dying and Ragnarok is approaching in the form of Hela (Cate Blanchett), his true first-born child. Odin tells Thor and Loki that their (previously unknown) sister was completely consumed by darkness and was sealed away but now she is returned. He apologizes to Thor for failing him before dying and disappearing. As soon as he’s gone, Hela emerges from her prison and engages the two in brief small talk. Seeing that she won’t be reasoned with, Thor throws Mjolnir towards her however the goddess easily catches and effortlessly destroys it. Loki, seeing they don’t stand a chance, asks to be returned to Asgard however Hela also enters the portal, expels Loki and then Thor from it at different points and then reaches Asgard. Arriving at the Bifrost Bridge, she quickly kills Volstagg (Ray Stevenson) and Fendral (Zachary Levi) before recruiting a terrified Skurge to her cause. She then heads to Asgard when she kills the entire palace guard single-handedly as well as Hogun (Tadanobu Asano).
Thor is deposited by the portal on a planet filled entirely by garbage and finds himself attacked by several scavengers. Now hammer-less, he is quickly overpowered before his attackers are scared off by the hard-drinking bounty hunter Valkyrie (Tessa Thompson). However she then captures Thor and takes him to the Grandmaster (Jeff Goldblum) who is delighted with his newest acquisition and decides to put him up against his champion fighter. Thor (now restrained with an implanted shock device) learns that Loki is also present and has been there for weeks (time moving far quicker on the Grandmaster’s planet) during which he has found favour with the Grandmaster. Not wishing to jeopardize his position, Loki pretends not to care and Thor is thrown in the dungeons where he befriends rock-creature Korg who explains that all who have gone up against the champion have been killed. Meanwhile, Hela heads down to Asgard’s vaults and uses a living flame to restore her entire army (it is revealed at this point that the Infinity Gauntlet that is kept in there is a fake). She then attempts to open a portal and conquer all the realms but the Bifrost sword has been taken by Heimdall who has been hiding in the hills and is now sheltering the escaping civillians from Asgard.
Thor is taken to the arena and put up against the champion who is revealed to be none other than the Incredible Hulk. Thor is overjoyed to see his old teammate and tries to make him transform back into Bruce Banner (Mark Ruffalo) however it doesn’t work and Hulk thrashes him (Loki is very unsettled to see the creature that gave him a sound beating during his attempted conquest of Earth). Eventually Thor stops holding back and begins to fight, at one point having a vision of Odin causing him to channel raw lightning. However just when he is about to win the Grandmaster, not wanting to see a crowd (and his own) favorite be beaten shocks Thor into submission. On Asgard, Hela has the remaining people rounded up and demands to know where the Bifrost sword is. When no-one comes forward, Hela tells Skurge to execute a random person. Skurge hesitates, but is still about to do it but before he can make the kill someone comes forward with Heimdall’s location.
Later, Thor speaks to Hulk privately (Hulk is now able to speak far more intelligently than he was able to in his last appearance) and learns that he hasn’t transformed back into Banner since leaving Earth two years earlier. He also finds that the Quinjet he left Earth with is still in one piece and could be used to escape. He also learns that Valkyrie is an Asgardian who was part of an elite all-female group who were sent up against Hela during her previous assault but were all killed (Valkyrie being the only survivor). Thor tries to convince her to help, but she initially refuses. Although Hulk is happy in his life and wants to stay, he does help Thor acquire the control device for his electronic restraint allowing him to remove it. Thor escapes from Hulk’s apartment and reaches the Quinjet, but is chased by Hulk who smashes it half apart. However Thor then plays Black Widow’s (Scarlett Johansson) last message to him and this causes Hulk to transform back into Bruce Banner. Thor explains to Banner, whose last memories are of Sokovia during Ultron’s offensive, what has happened. Banner, unable to believe Hulk was able to remain in control for two years, doesn’t want to transform again knowing that if he does then he’ll likely remain as Hulk forever. Valkyrie meets up with Loki and the two engage in a brief fight, and after Loki learns where she comes from he uses his powers to make her remember her last encounter with Hela. This causes Valkyrie to have a change of heart and she decides to help Thor return to Asgard, and shows her good will by beating and chaining up Loki. Reuniting, Thor and Loki head down to steal a ship however Loki attempts to betray Thor to the Grandmaster. Thor however had expected this and has instead put the shocking device onto Loki’s back. Thor tells his brother he’d hoped he would at least show some capacity for growth and even begin to change for the better, but now he understands Loki will always be a trickster. He then leaves the shocking device turned on with the remote just out of reach.
Thor, Banner and Valkyrie steal the Grandmaster’s party/orgy ship and, escaping the Grandmaster’s clutches, leave through a passageway known as the Devil’s Anus. Reaching Asgard just as Hela is about to destroy the remaining population who had attempted to escape through the Bifrost Bridge, Thor engages her in a vicious battle but is still overpowered and loses an eye. Feeling he is useless without his hammer, Thor has a vision of Odin who explans to his son that the hammer simply channeled his powers reminding him he is the God of Thunder. Odin also tells him that anywhere can be Asgard, as long as its people survive so will the society. Now realizing his full abilities, Thor unleashes a massive lightning bolt sending Hela flying. As Valkyrie and Heimdall attempt to hold off Hela’s army, Loki unites with Korg and other escaping fighters and procures a ship which he uses to evacuate the Asgardians. Banner also transforms back into Hulk to fight one of Hela’s gigantic hounds. Skurge, feeling guilt over having ever gone along with Hela, sacrifices himself to ensure the ship manages to get away.
Thor unites with Valkyrie and Loki knowing Hela will soon be back as she is only growing stronger from Asgard’s power. Thor suddenly realizes that he cannot stop Ragnarok but must instead bring it about, and sends Loki down to the vaults to throw Surtur’s skull into the living flame. Loki does so and escapes (it’s also heavily implied that he takes the chance to steal the Tessaract) just as Surtur is reborn and starts laying waste to the kingdom as well as easily killing Hela. Thor escapes with Loki, Hulk, Heimdall, Valkyrie, Korg and the surviving civillians/prisoners just before Asgard is completely decimated. Although Thor is upset about the destruction of his home, he knows that he had to do it to prevent the extinction of his people. He then finally meets his destiny and takes the ‘throne’ (really, the captain’s chair on the bridge) where his first order is to return to Earth.
Loki worries over Thor’s decision to return to Earth knowing he won’t be very welcome there since on his last visit he tried to take over the planet. Thor assures his brother he feels everything will be fine, just as a menacing looking ship (which is gigantic compared to theirs) appears through the window.
The Grandmaster, who had been chasing Thor, crashes on the garbage planet where he is confronted by the scavengers who are also a bunch of former slaves. He congratulates them on their revolt and agrees to call it a tie.