Count Nefaria addresses the captive X-Men in their prison cell, deep within his fortress. He plans to “steal the nation’s capital”. Just like the X-Men fell before the might of the revived Maggia, so shall soon grovel all of America before Nefaria. The count offers the X-Men to join him or else he will be forced to destroy them.
The Angel and Iceman immediately refuse this offer and actually think the villain mad, for how can somebody steal an entire city, while Cyclops suspects that Nefaria indeed will back up his claim. Nefaria gloats that whether they join him or not, the world will blame them for his crimes. He announces that they have one hour to decide his offer and leaves.
From another room inside the complex, Nefaria starts with his plans by working on a strange machine, that will seal off Washington. Indeed, as he manipulates the control, citizens in the capital of the United States see small flakes in their air. One wonders why it is snowing in June, but another points out that the particles are glowing and is some sort of crystallized matter. Minutes later, they have combined into a solid, transparent dome over Washington, cutting the city off from the outside. A plane nearly crashes into it, while on the streets cars can go neither in nor out of Washington.
The people are confused. Some suspect it’s a new plan by the government to make Washington attack-proof and the local police do not know what to tell the confused citizens. Inside the Capitol, the senators decide to call the Pentagon. A firefighter tries his axes on the barrier, a construction worker probes it a pneumatic drill, and the military even uses dynamite, but nothing penetrates the all-encompassing dome. All they can do is wait for whoever constructed the barrier to get in contact with them.
From afar, Nefaria is satisfied with himself. All is going well and he activates the next phase of his scheme.
Seconds later, the five X-Men arrive in front of the Capitol. They tell a guard that has come about the shield that covers the city. As he saw them in battle against the Sentinels, he believes that if anybody can penetrate the dome, it is they, so he lets them pass. However, once in front of the Special Committee meeting in the building, Cyclops reveals that they are not there to help, but to make an ultimatum. They want 100 million dollars or else the force dome will absorb all oxygen inside within three hours.
The councilman says that they can’t decide this alone, they have to call the entire Congress. The X-Men, already on their way out of the office, tell him to hurry. In three hours one of them will return to pick up the money from the Senate’s representative on the Capitol steps. A few guards try to stop the five teenagers, but suddenly they vanish into thin air, leaving the guards wondering if that is yet another their mutant abilities.
While all this is going on, the real X-Men, for these were just illusions, are still chained in their prison. Marvel Girl tries to use her telekinesis on the Beast’s cuffs, but she fails. Even with her fullest concentration she is unable to open them without first having studied the locks. She wishes they could get in contact with Xavier.
Back in Westchester, the professor has sealed off his brain from any outside disturbances, as he wants to use the X-Men’s vacation for perfecting his latest inventions. However, he forgot “about such mundane a thing as a telephone”, which starts ringing. Interrupted from his work, Xavier picks up the call. It’s General Fredericks, who informs him of the X-Men blackmailing Washington. The military would like the professor to function as civilian adviser once more. Xavier agrees to meet the general within the hour and hangs up the phone. He knows his students can’t be involved in this, but the general must have a good reason to say it is they, so he tries to contact the five teenagers. He receives no answer and understands that the young mutants must be some distance away. He tries again.
At the same time, Cyclops has an idea and asks Jean to try to bypass the metal band covering his head and open his visor slightly. Already strained from her earlier efforts to unlock the chains, Jean says she’ll give her best, especially as the fate of the city is at stake. She manages what Cyclops asks of her and the visor opens enough for him to release an optic beam to blast away the headband. Next, he fires on his own bonds and then releases the rest of his team. Just as they are about to leave the dungeon and confront Nefaria, Xavier establishes telepathic contact with them. He fills them in on their exact location and gives his students further instructions.
Nefaria follows the events in Washington on a giant tele-screen. He talks to himself that, finally, the Senate has agreed to his terms and that the money will be ready at the end of the three-hour period. Suddenly, he becomes aware of the X-Men behind him. However, they don’t want to fight him, but join him, and ask what their percentage of the take is. Cyclops claims their reasoning for switching sides is that humans hate then anyway, so why not get revenge on them and make money at the same time?
Nefaria congratulates them on their decision, but also warns them that the crystalline dome has been designed in such a way that only he can manipulate the dials to dissipate it, just in case should the X-Men think of deceiving him. The Count explain the plan to the X-Men and then leads them to a harmless looking milk truck that will take them to a location where they can enter the trapped city.
Not fully trusting the X-Men, Nefaria radios some of his operatives to start with “Plan C” and a second vehicle sets out to Washington. Inside are Plantman, Unicorn, Porcupine, Eel and the Scarecrow. They arrive at the outer rim of the force field before the X-Men do, as they are supposed to watch them. However, the five villains have other plans. They have decided to unite against Nefaria and intend to seize the 100 million dollars for themselves. They hide behind some bushes, as they know the X-Men will arrive soon.
Meanwhile, Professor Xavier arrives outside Washington, where he is briefed by General Fredericks, who is hoping that the expert on mutants might have an idea how to penetrate the force dome. Xavier ensures he’ll do his best, though he first wants to know how the general is certain that the X-Men are behind this and not somebody else framing them. The stressed general gets angry. The radio reports coming out of the city verify that it was indeed the X-Men who walked into the Capitol. Through the telepathic conversation with his students, the professor already knows that these were only illusions created by Nefaria, but he can’t reveal this to the general. He apologizes and asks Fredericks to give him a few minutes to think about the entire situation.
Xavier prepares himself for an astral journey, though the soldier present think that he has fallen asleep from the excitement. The professor mentally reaches the stronghold of Nefaria and observes the Count in his command center, where he observes the van carrying the X-Men on his video screen. Xavier witnesses Nefaria creating an opening for the van to pass through the dome and also learns that he plans to use the money to rebuild the Maggia into the most powerful criminal organization on Earth. The Professor wonders how he can be stopped.
The X-Men have left the truck and stand in front of the force field. Right on cue, a hole opens to let the quintet enter and, once they are through the wall, seals off again. Iceman is impressed by the genius of Nefaria to design such a thing, though Cyclops reminds him to stay alert. As the team proceeds to pick up the ransom for the Count, they are unaware of being observed by several soldiers, who in turn are watched by the five super-villains. The Plantman asks when they will make their move and the others agree it is better to wait. They’ll let the X-Men do their dirty work and pick up the money, only to steal it from them later on. That way, it will be the mutants who are sought by the police and not they.
Minutes later, a Congressman is standing in front of the Capitol, with a briefcase full of special large-denomination certificates equaling the demanded amount of money. The Angel dives down, wrests the briefcase from the startled politician, and heads back to where he came from. However, a guard witnessed the scene and, apparently not knowing what’s at stake, pulls his gun to shoot the “thief”. The Congressman is too late to stop the guard, though Iceman is not as he encases the gun in a block of ice.
The X-Men make their escape and head back to the perimeter of the city. So far, everything is going according to Nefaria’s schedule and they hope that Xavier is telepathically keeping tabs on them. As the five mutants pass a construction site, they are spotted by a group of angry civilians. Intending to show the muties what they think of traitors, the men start throwing bricks at them, making Warren drop the briefcase, though Scott catches it. Cyclops, Marvel Girl and Iceman can all use their powers to deflect the bricks hurled at them, and the Angel rises out of reach, though the Beast is surrounded. He has no other option than to climb up the Washington monument. Warren could fly him away, but what about the others, who don’t dare to use their abilities in offensive manners?
Unexpected help arrives in the form of the five super-villains, who have grown impatient. The Scarecrow commands his birds to attack the humans and Porcupine releases some tear gas through his quills. The Unicorn calls the X-Men over to join them, where Nefaria is already again opening an escape hatch in the force wall. Suddenly, Plantman causes some vines to entangle the Beast’s feet, making him drop the briefcase. The Eel tries to pick it up, but is zapped by the Unicorn, who never intended to share with the other four. He stuns his former partner and flees with the prize.
Within his castle, Nefaria is furious over the Unicorn’s betrayal and announces he will pay for this. Indeed, the villain’s escape is stopped by a few tanks emerging out of a fog bank. Behind him, the way is cut off by the X-Men. The Unicorn knows he has a better chance against the military and releases his force beam at a tank. Surprisingly, it passes through it and the Unicorn realizes that the tanks are just a projection from within Nefaria’s stronghold. With his escape route again wide open, the Unicorn activates some tiny rocketlifts in his boots and takes to the air, too fast for the Angel to follow.
(a few minutes earlier)
Outside the giant dome, a soldier tells general Fredericks that the three hours are up, and the people inside are still alive. The ultimatum was a fraud. Xavier says that he suspected as much, but the general is too busy to chat with him, as he orders his troops to shoot the X-Men on sight. The Professor understands that his services are no longer needed and takes to a nearby hotel. The staff is all excited and anxious about the events outside, but Xavier asks to be wheeled to his room as he is very exhausted.
The Unicorn rockets away, though he again spots the army in his way. He thinks that Nefaria is a fool to try the same illusion trick twice. However, these tanks are the real deal as the villain painfully learns when he is shot out of the sky, making him drop the briefcase. Cyclops picks it up, while the soldiers are unsure why the various super-powered beings are fighting each other. Not wanting to take any chances they decide to attack all of them, though Iceman already has frozen the tank’s gun barrel, and the Angel and the Beast engage most of the footsoldiers. Scott hands Jean the bag with the money and tells her take it to the rendezvous point while he helps the others.
Again hidden in the bushes, Eel, Porcupine, Plantman and the Scarecrow observed the last scene and plan to tackle the redheaded mutant. Before they can do so, they are too spotted by the military. As their direct orders were to capture the X-Men – dead or alive - the soldiers think they should detain these costumed kooks too. Easier said than done, as the Eel is too slippery to be held, the Scarecrow is agile and summons his birds for further defense, and the Porcupine’s quills turn razor-sharp. Camouflaged by his green costume, the Plantman is overlooked and he uses the chance to increase the vegetation’s growth of the entire area with a ray gun. While the soldiers get entangled in the newly grown jungle, the four villains escape, without the money or the Unicorn, but at least free.
The X-Men used the distraction to get away, but they are too late to catch the truck that was supposed to take them back to Nefaria’s hideout. It has already departed, with only Marvel Girl and, more importantly, the money inside. However, as it is still within visual range, Cyclops orders the Angel to follow.
Still hidden between the bushes he fell into, which apparently cushioned his impact, the Unicorn does not dare to come out. His power reserves are down and there is still too much military in the area, so he will lie low and wait untill they have left the area.
In his fortress, Nefaria is anxious for the truck with Marvel Girl to return. His great plan worked and, with the 100 million dollars in the briefcase, he can re-establish the Maggia. What the Count is unaware of is a cab arriving at a side-entrance of the castle. A mysterious stranger gets out. He is disguised with a hat, sunglasses and a scarf. The man claims to have business with their master, but the guards refuse to let them through. Somehow, he renders the two of them unable to move and, as he walks by them, he tells the confused guards that, in another second, they will also be unable to talk as well. He doesn’t want Nefaria to be forewarned of his arrival.
Elsewhere, the truck arrives and Marvel Girl brings the briefcase into the command center. Nefaria is eager to get it, but the female X-Man holds him back telekinetically and tells him that he has to remove the crystalline dome around Washington first. The Count pretends that he already manipulated the dome to not destroy the oxygen inside, however the mechanism will be reactivated if he does push a proper sequence of buttons every five minutes. Jean is unsure, but has no other choice but to trust him and release him. She places the briefcase on a table, right as the stranger enters the room as well. Without a word, the ominous figure turns to Nefaria’s machines, manipulating its delicate controls as if he designed them. Nefaria is shocked and wonders how anyone but him could have such knowledge of the device, but he can only watch, as Marvel Girl again holds him in place with her mental power. The stranger not only lowers the force dome, but also types in sequences that will destroy the evil machine once and for all.
Right then, the other X-Men burst in through a window. They are concerned for Jean’s wellbeing, but she tells them she is fine. Cyclops asks where the villain and the money are and Marvel Girl turns around to see that the Count has used the team’s entrance to escape with the prize. The stranger points out through another window and tells the mutants that Nefaria has just boarded his freighter, though there is no need to follow him. As the teenagers look out too, they see the Unicorn flying to the ship. They think they have to do something before the freighter reaches the three-mile limit.
The stranger once more promises that the ship won’t reach international waters. He takes off his disguise – it’s none other than Professor Xavier. The team wonders why he is walking and he lifts his coat to show them a portable device that he has secretly been working on. It’s a transistory power source for lightweight flexible metal braces for his legs. Still puzzled by this turn of events, Iceman wants to know why they are not trying to catch up with the villains and retrieve the money, but the Professor points to under the table. The briefcase is lying there.
Aboard the ship, Nefaria is holding a second, identical briefcase. He is already making plans to use the fortune inside when, suddenly, the Unicorn bursts in. His power horn is exhausted, but he is eager to fight the Count anyway. Nefaria tells him there is no need; it’s more than enough money for both of them. Suddenly though, the briefcase vanishes. It was just another illusion of Nefaria’s machine.
Back in the fortress, Xavier explains that he used the Count’s own invention against him. Additionally, he alerted the Coast Guard who are already on their way to intercept the ship. The team is happy that everything turned out fine.
Xavier remembers that this morning a letter arrived for Jean and he pulls it from his coat to hand it to her. She quickly reads it and gets very silent. The others ask her what is wrong with her, and Jean announces that tomorrow she has to leave the X-Men – forever.