The Escape from Muspelheim was a successful escape attempt orchestrated by Thor after extracting information about Ragnarök from the Fire Demon Surtur.
Background
Thor has been captured by mysterious enemy forces. He rambles towards a skeleton sharing his cage about seeking the Infinity Stones, but having found nothing. Thor said that sometimes you have to get captured to get a straight answer out of someone with that someone being Surtur. Thor managed to get freed from the cage, and arrives at Surtur's world, Muspelheim in which the latter taunts him with the knowledge that Odin is no longer on Asgard and Thor's absence leaves it vulnerable.
Surtur announced that Ragnarök is coming to Asgard at his hand and there is nothing Thor can do to stop it, while foolishly confessing that his crown is the source of his powers.[1]
Battle
- "I am Asgard's doom and so are you. All will suffer. All will burn."
"Wow. That's intense. To be honest, seeing you grow really big and set fire to a planet would be quite the spectacle. But it looks like I'm gonna have to choose option B where I bust out of these chains, knock that tiara off your head, and stash you away into Asgard's vault." - ―Surtur and Thor[src]
Thor took a big cue to call in for his loyal hammer, Mjølnir, causing Surtur to call for his creatures, leading to a lengthy battle between Thor and Surtur's army.
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Thor effortlessly defeated Surtur's army with Mjølnir, before summoning a large blast of lightning to defeat the rest of his attackers. Surtur attacked Thor with the Twilight Sword, but Mjølnir protected Thor from its fiery blasts. Thor concentrated his attack on Surtur's crown, striking it several times with Mjølnir before causing it to come off, absorbing both Surtur and the Twilight Sword as it hit the ground before Thor picked it up and chained it to his back. Thor tried to return to Asgard, however Heimdall does not respond. His replacement, Skurge, only notices Thor's call when one of the women he is trying to impress points it out.
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Returning to Asgard, the Fire Dragon attempted to return to the place with Thor himself and to finish the job, but was decapitated by the beam from the Bifrost Bridge, causing its blood to be spilled on Skurge and the women.[1]
Aftermath
Thor returns to the Royal Palace of Valaskjalf with the Crown of Surtur
Thor was told that Heimdall had been charged with negligence of duty and declared a traitor after he disappeared before the trial. Thor arrived at the Royal Palace of Valaskjalf just in time to watch a play "retelling" Loki's supposed sacrifice, with Loki, still disguised as Odin, watching and enjoying it. After ordering Surtur's crown to be placed in the vault, Thor forces Loki to drop his disguise and help him find Odin, the two eventually reuniting with their father in Norway.[1]