Spider-Man joins the X-Men to take down Juggernaut! The power of the Cyttorak grows in the mutants' fiercest foe, as all sides scramble to subdue Cain Marko. Spider-Man has a change of heart about the X-Men- but why?
As Spider-Man enters his room from the ceiling, Mrs. Muggins is calling Peter Parker at his apartment looking for the rental. She says she has been watching his doors and he hasn't come out since he entered so she knows he is still inside. So, Peter goes back to the ceiling to escape, but his new neighbors are outside having a sun bath - three girls that live together - Candi, Bambi and Randi - wearing bikinis. When he goes back to his room, Mrs. Muggins is about to open the door. He manages to take off his suit and get a towel just in time. When she enters he starts to complain about the girls making noises on top of his apartment, trying to make an excuse to her, as she says the blonde one is her niece Candi and that they have already payed the rental. Peter says he will pay on Thursday. When she leaves he thinks about Aunt May's birthday present he has to buy and he has no money.
Above an Asiatic jungle an airplane is flying over when the doors open and Juggernaut jumps off, without a parachute. They are just above the ruins of the Temple of Cyttorak in Korea. He fells on the ground on top of a Korean War tank and then the army shoot at him, with no effects. He defeats the army alone and destroy a couple of tanks in the process. Juggernaut thinks about Spider-Man who had trapped him in the ground with cement while he is about to defeat Madame Web for Black Tom. It took six months for him to escape and now he wants to pay his debts with Black Tom. That's why he is in Korea, to take the Crimson Gem of Cyttorak and give more power to Tom.
Back to Manhattan, Peter still doesn't get any money because Robbie is tired of his Spider-Man's pictures. When he is walking to his apartment the three girls are outside angry at him because his complains about their noise. When he says he is a photographer they ask him to take some photos of them, because they want to be models and don't have a book yet.
In the X-Mansion, Colossus and Rogue are training in the Danger Room and Nightcrawler is leading them. They aren't good enough for Nightcrawler and have to try again. After another session they have improved their marks but it isn't good enough again, because one of the missiles hit Rogue. It ripped her clothes so she can't touch anyone because of her powers. Nightcrawler says they are getting better and suddenly Rachel talks to them mentally asking for dinner. During dinner they watch Juggernaut on television destroying the Korean troops and then walking from the cave with the Crimson Gem. They explain to Rachel that he is an old foe of X-Men, brother of Professor Xavier and about the power of the Ruby. Rachel thinks to herself that in her future, Juggernaut did the same think to give power to Black Tom, would he do it again?
In Manhattan Peter finds a hat sale in the newspaper, but he still doesn't have the money to buy it for Aunt May. Then he also watches Juggernaut on television and decides to go after him. He thinks about how he used to like the black suit but it is better without it. He also thinks about Black Cat, Mary Jane and the baby of Harry Osborn and Liz that is about to born. Meanwhile Juggernaut is in one of the most expensive hotel room of the city, celebrating Black Tom's birthday. He gives the Crimson Gem as a gift to his only friend and when Tom opens the box and touches the Gem, he starts to glow and grow to the size of Juggernaut himself. He shouts at Juggernaut saying he doesn't want to be that big and want to go back to normal and then push Juggernaut through the window toward the streets.
The X-Men use Cerebro to find Black Tom because of what Rachel said and they go after his location.
Juggernaut gets mad after being hit by Tom and goes after him climbing the building. When he gets upstairs he also push Black Tom towards the ground from the window and jumps after him. They start to fight and destroy the street and blows up a gasoline truck. Then Juggernaut realizes he is feeling the fire and Tom's punches, so something is wrong with him. Tom stated that he actually is smaller than before and they conclude that the Gem had shared its powers on both.
Spider-Man hears the explosion and goes after the sound, just to find two indestructible men. He sneaks towards them to take some pictures to sell to Robbie and make some money, but Juggernaut sees him and want revenge on him. Spider-Man easily defeats Juggernaut now he is weaker, but then Tom decides he actually is his friend and helps him at the fight. Tom punches the ground and brakes a wall, dropping Peter's camera. Then Cain and Tom team-up to fight Spider-Man. Spider-Man makes a huge web to trap them both and while Juggernaut is trying to destroy it, Spider-Man pull a sewer cap from above him so he falls over Black Tom and they both destroy a building on top of them. But it doesn't stop them and they finally catch Spider.
Suddenly the X-Men arrive. Rachel is still thoughtful about the Black Tom from her future and what he had done for her.
They all start a huge fight, with Black Tom using his mutant powers together with his new strength and Juggernaut a little bit weaker but still dangerous versus Spider-Man, Rogue, Colossus, Nightcrawler and Rachel.
Colossus throw Tom away but then he grabs an entire building and drops it on the X-Men and a bunch of innocent people. The X-Men manage to save everyone with the help of Rachel, who realizes that this is not her past and that here Black Tom is a bad guy.
Black Tom is about to kill Nightcrawler with his hands when Rogue decides to touch him and absorb his powers. Tom passes out and get smaller, but Rogue grows bigger with Cyttorak's power. Rogue now has the power to fight Juggernaut face to face and they start throwing punches. Rachel tries to get inside Juggernaut's mind but his molten helmet prevents it. Suddenly Rogue lost her new powers but it doesn't come back neither to Tom or Cain.
Colossus manages to take off the helmet but Juggernaut has a second helmet under the first one, and so Rachel can't attack him and he will kill Rogue. At last Rogue touches him and absorbs his powers, together with his memories. His father beating him, his young life with Xavier, the discover of Cyttorak's Gem and everything that had made him what he is now. Rogue starts to cry and get insane, attacking his friends with Juggernaut's powers. Suddenly the power goes away and Rogue calms down, but the power goes back to the Gem and Cain touches it again, regaining all his powers.
Then Juggernaut throws the Gem to the sky with all his strength, putting it orbiting in the space. Black Tom and Juggernaut runs away by the sewers. Cain says he is sorry for screwing up Tom's birthday but the other answer saying this was the best fight he has ever had.
The X-Men shake hands with Spider-Man and before the cops arrive they vanishes, because they are all not welcome in the city. Rachel levitates, Nightcrawler disappears in the air and Rogue flies away carrying Colossus, while Spider-Man crawls over a building.
At the end, when Peter Parker goes to work in order to sell his photos of the fight to Robbie, the film was ruined and the only good photos he has is that with the girls on top of his building wearing bikinis. Fortunately this is just the right type of photos Robbie is needing to finish the newspaper of the day after. So Peter gets his money and can finally pay his rent and get a hat for his aunt.