A man is moving clandestinely inside a chemical factory. He is content; he has found a job with a good salary: he is working as an industrial saboteur. His mission is basically to destroy his employer’s competitors. Suddenly, he looks at his watch: the thermal bomb has been set to explode at 12:10. However, it is 12:10! In a last horrible moment, the man realizes why he was betrayed by his employers: they wanted to assure he would never reveal their dirty business to anyone… and the only way to silence the saboteur they hired would be by death! As the man is burnt by the chemicals, he swears that, if he survives, his revenge will be terrible.
A room, a studio, where the millionaire businessman Howard Anthony Stark once held his young son on his knees, while his beautiful wife, Maria, played Chopin in the piano. The same music can be now heard, though not from the piano but from the radio: from a wonderful stereo system. Beast is delighted to listen to the music through earphones plugged into the stereo system. Suddenly, though, the music program is interrupted. Infuriated, Beast turns on the TV monitor to see what’s going on.
On TV, a reporter is informing the viewers that the Human Torch, youngest member of the Fantastic Four, has just arrived to New Jersey, responding to the mayor’s emergency call. Beast is puzzled: why did they interrupt the program? This must not be a normal fire.
On the screen, Human Torch flies towards the fire. The Torch’s abilities are amazing; however, he seems to face some difficulties in coping with the fire. Indeed, at that moment, the infernal fire seemingly drains Johnny Storm of his flames and the Torch almost collapses on the ground. A moment later, a powerless Johnny uses his last flame to throw himself on the hands of the firemen, finally safe. The reporter is amazed to see that the Torch seems to have been in some sort of shock. At that moment, unnoticed by the people present but discernible to TV viewers, a face bearing a mocking smile can be seen materializing in the flames!
Beast notices the mocking face and is now certain this fire can’t be normal: not a fire that could siphon Human Torch’s flames. Beast rushes to the dining-room where he finds the other Avengers eating sandwiches and drinking tea. Captain America offers him a drink. However, Hank tells him he has bad news and switches the TV on. The others are puzzled by his doing so.
Wasp tells him all they can see are flames, the same image that all the local stations are broadcasting. Cap stresses the fact it is a fire with chemicals that seems to have gone out of control. Vision asks Beast to inform them what the Avengers have to do this. Beast is furious they can’t realize what is going on there. Wonder Man tells him they all know he’s acting weird sometimes but he must explain the situation to them. Beast explains his suspicions that this fire is… alive!
The Avengers watch more closely, as Human Torch reports on TV that this not a natural fire: the flames spread throughout the city in an unnatural manner, burning down one chemical factory of Liquagas Company Complex after the after, as though this fire has been orchestrated by a madman. Suddenly, Wasp screams she can see a face materializing in the flames. Cap assures her they can all see it.
Cap suggests to the others they should go and check out the situation. After all, only the Human Torch is there and he has failed. Carrying a fire extinguisher, Jarvis assures Captain America he himself is also willing to do anything to help the situation!
In short time, the jet, constructed for Avengers by the Stark International, courtesy of Tony Stark (Iron Man’s double identity) flies above New Jersey, with Iron Man, Wonder Man and the Vision flying outside the ship. They can easily discern their destination in this dark night: it’s the huge raging fire up ahead, a real inferno! The Vision remarks that the flames are getting close to the liquid natural gas tanks of some warehouses below: the result of that explosion could be the equivalent of a nuclear disaster. Through a device in his helmet, Iron Man reports to Captain America, who’s piloting the ship that the extreme temperature could ignite the liquid natural gas, although both the fire and the temperature seem to be controlled within the factory area, but not outside it.
Suddenly, Beast urges Cap to warn the others outside to fly higher, since temperature is rising very quickly. The three flying Avengers seem to be lost in the flames. Scarlet Witch screams her husband’s name as Wasp assures her the Vision must be okay. Cap has worse news: the jet is going down!
As the jet starts spiraling downwards, Cap reclaims control of the ship but fears they may still crash down before he can get it up again. Suddenly, everyone is startled to realize that the ship seems to be frozen in mid-air! Soon, they find out what has transpired: Human Torch is using his power to create a layer of hot air under the jet, preventing its fall.
Moments later, the Torch helps the jet land safely on the ground. Captain America asks the Torch more information about what happened. Johnny explains he can’t approach the inferno; his powers where drained when he did, rendering him powerless. Meanwhile, Scarlet Witch is worried that the Vision, Iron Man and Wonder Man haven’t shown up since they were surrounded by the fire.
Up in the sky, Wonder Man is horrified to see he’s on fire. Iron Man implores him to use his belt jets to fly up and away; Tony himself and the Vision can protect themselves thanks to their mechanical systems. Wonder Man refuses to act cowardly, however Tony does not leave him a choice and blasts him away with a beam to save him. Together, Iron Man and Vision rush into the heart of the fire, although Tony confesses that even the cooling units of his armor can’t fully counterbalance the extreme heat he starts to feel.
Beast is shocked to see Wonder Man falling from the sky. The firemen grab the safety net, although Beast assures them the impact won’t harm Simon. Indeed, thanks to his invulnerability, he breaks through the net and blasts a huge hole on the ground.
Without wasting time, the Avengers put on “super-dense asbestos” fire resistant suits that can keep them alive for quite some time into that inferno, until they find out who’s responsible for all this. Janet is enraged to see that there is no suit that can fit her diminutive insect-like Wasp size. Apparently, she’ll have to stay behind and can’t help but feel like a fifth wheel. Human Torch assures her he knows how she feels but Janet is not consoled by that remark.
The remaining Avengers rush into the fire. Jocasta tries to find an adjective to describe the fire, to which Cap suggests “beautiful.” Wanda, on the other hand, does not find it beautiful; she finds it horrible and unnatural and wonders whether her husband can still be alive in that living hell. Jocasta assures her he’s unharmed, because he’s just approaching them.
The Vision comes near them, asking them to forgive him if he gave them reason to worry. He’s now in an intangible form. He can’t return to normal density without risking instantaneous incineration. Wanda rejoices in seeing him alive and well. The others ask him about Iron Man. Vision informs them Tony proceeded in this hell as far as he could and then ensured his survival. Vision leads them to Iron Man, who has used the cooling unit of his armor and trapped himself in a deep freeze state in order to survive. Before that happened, they had apparently confronted the entity responsible for creating this fire but were defeated.
The Avengers start moving further inside but Vision refuses to follow, instead informing them that the enemy can be found at the end of the tunnel. Jocasta explains to Scarlet Witch that her husband can’t follow because he’s well aware the high temperature will destroy his synthetic body. He should better remain behind to guard the helpless Iron Man.
Finally, the team meets the enemy. The entity, which seems to be made entirely of fire, calls himself Pyron and tells them he expected the rest of the Avengers to show up, after defeating Vision and Iron Man. He assures them he fears nobody; he actually desires an audience to watch when he exacts his revenge.
Cap realizes this being must have been human but he is now somehow composed of incandescent coal that releases heat. Cap wonders aloud what Pyron hopes to win by creating this inferno. Pyron replies that he wants revenge from those people who paid him to burn down a factory complex that belongs to their competitors. His former employers betrayed him, setting things up so that he could die in the explosion. However, he survived. The chemicals gave him a new life as Pyron the Thermal Man. Now his former employers that own the Liquigas Company will see their profits turn into ashes!
Cap remarks it’s difficult to show sympathy towards an arsonist, especially one that endangers the entire Jersey. He hurls his famous shield on Pyron, only for the latter to snatch it. Pyron wants to find out if Cap’s shield is as indestructible as is rumored to be; he releases intense heat on it.
Wonder Man and Beast try to strike Pyron but, at Pyron’s touch, their suits begin to smolder. Jocasta notices this and releases her optic blasts against the Thermal Man, who immediately screams in pain. The Avengers are happy to see they finally have a weapon to strike him with, however it comes with a price. Jocasta’s optic blasts broke through the protective mask of her suit and now, exposed as she is in the heat, her titanium steel frame starts melting. Jocasta assures them she feels no pain, given she’s not human, but she has been indeed damaged.
Cap urges them to remove Jocasta from the area before she’s entirely ruined. Wanda believes that Jocasta could be their only hope at defeating Pyron but Beast assures her she won’t have a second opportunity to strike him unless she survives – and she can’t survive now, exposed to the increasingly higher temperature. Wonder Man carries Jocasta in his arms and walks away, despite her protests. He assures her he also felt bad when Iron Man told him to leave but. if he didn’t, he wouldn’t be alive now to rescue her.
Pyron is delighted to see only three Avengers standing, the three most powerless ones in his opinion. Wanda furiously releases her magical hexes and suddenly geysers of water spring up from the ground. Within seconds, Pyron transforms the waterspouts into pillars of fire. The three Avengers realize they are doomed.
Outside, Wasp sees Wonder Man approach with Jocasta and asks him what happened. Wonder Man tells her all about the origin and intentions of Pyron. Suddenly, the president of Liquigas approaches him, demanding him and the Avengers to stop immediately. Furious, Wonder Man grabs him and reveals to everyone present that Pyron was an arsonist sabotaging rivaling factories, until Liquigas arranged the thermite explosives to explode in the hands of their saboteur so as to silence him forever, unaware that the chemicals would transform him into this monster.
As the president of Liquigas is promptly arrested, Human Torch contemplates going inside the inferno to help the Avengers, no matter how suicidal this may be. However, the Wasp has already gone inside, wearing a suit made of asbestos.
Janet follows the tunnel of fire, despite Vision’s pleadings to go no further. Within the glove of her suit, Janet clasps a silver capsule. As she approaches the team, they all tell her to leave and call Thor, rather than die there with them. Wasp tells them she has the way to defeat Pyron. The Thermal Man is delighted he’ll kill one more.
Turning into her Wasp form, Janet breaks out of her suit, realizing she only has few precious moments to survive. Carrying a chemical foam capsule, she hurls it on Pyron. As the foam seeps into his pores, he screams, falls on the ground and reverts on his human form, with the inferno being snuffed away, while Wasp collapses, bidding her farewells on her teammates. The Avengers assure her she’s not going to die. They are all astounded by the fact Pyron was defeated by the smallest of their group.
A little while later, while the Avengers finally take a breath, Janet looks sad. When asked by Cap why she looks so troubled, she shares her concern over how she’s going to explain her tan to Hank: it’s December!