A bank is being robbed, and the robbers are dressed like the X-Men. The police are no match for the masked mutant robbers and they get away in a stolen vehicle.
Meanwhile, Scott has packed his suitcase and is leaving the X-Men. He fears that his optic blasts are a threat to everyone around him, including those he loves. He seeks to be cured of his blasts and departs quietly, leaving only a note behind to explain his absence.
The other X-Men are hanging out in the study, unaware of Scott’s “unheralded departure”. On the news, they learn that they are being accused of robbing the bank.
Hank goes to inform Professor Xavier, who is finishing setting up the new Cerebro. Xavier is aware of the news and has “telepathically commanded the others to join them”. Cerebro reveals the two robbers to be the Blob and Unus, the Untouchable. Hank is furious that Unus went back on his word after promising the X-Men he will stop his evil ways.
Xavier cautions the X-Men on approaching the Blob and Unus as “[he] sense[s] that a third entity has masterminded this entire scheme o discredit [them]”. Unfortunately, Xavier is unable to detect this “mastermind” as he is out of range for Cerebro.
Suddenly, Jean realises that Scott is missing. Bobby rushes out of the room in search of Scott, only to return with Scott’s note. Xavier tells the team that they do not have time to dwell on Scott’s departure and they have to act quickly to stop the Blob and Unus. Jean hides her anguish at the thought of not being able to see Scott again. Xavier is going to work on a “mechanical memory-inducer to quickly penetrate [their] foe’s defences” and identify the mastermind.
The mastermind turns out to be Lucifer. Lucifer has been seeking out the Blob and Unus to help him carry out his evil plan. He bides his time for the Blob and Unus to meet by chance. And they do so at a wrestling tournament. After wrestling each other, the Blob and Unus both come to the consensus that they are both mutants. They form a friendship over common ground: hatred for the X-Men. Together, they hatch a plan to frame the X-Men.
While the Blob and Unus are robbing their second bank in their X-Men disguise, Scott witnesses the robbery. Despite vowing never to use his powers again, Scott overhears the crowd bad-mouthing the X-Men and decides to help clear the X-Men’s name. Scott changes into his X-Men uniform, and intends to show the crowd he is a real X-Men and that the Blob and Unus are imposters.
But the Blob and Unus have ideas of their own and try to convince the crowd that Cyclops is one of them as well and up to no good. Even though Cyclops tries his hardest to stop the Blob and Unus, he fails to convince the crowd that the X-Men are the good guys. He retreats in shame, not wanting to further “discredit” the X-Men. Cyclops decides to return to the X-Men to help his team mates.
Lucifer observes the situation from his lair and is disappointed that only one X-Men “dare[s] to attack [his] costumed dupes”. Just then, Beast, Iceman and Angel show up and Lucifer expresses relief.
As the Blob and Unus gather their loot, Beast attacks Unus with the ray gun that once defeated Unus. But Unus is now immune to the ray gun, thanks to Lucifer. Iceman tries to help Beast. But the crowd has had enough and start attacking the X-Men, from old ladies to policemen. Beast, Iceman and Angel escape the crowd, and are rejoined by Cyclops. The team is glad to see Cyclops has returned.
Back at his lair, Lucifer finds out that Xavier has “penetrated [his] mental screen”. He prepares his assault on Xavier, using a cannon to blast a “potent beam” that will home in on Xavier’s signature. Xavier is affected by the blast and appears to be in a comatose state. He is barely able to telepathically communicate with Marvel Girl.
Once Marvel Girl is reassured that Xavier is still alive, she follows his instructions and uses the “mental-wave amplifier” to be able to communicate more clearly with him. Xavier recounts his first encounter with Lucifer to Marvel Girl, wherein they will learn how to defeat Lucifer.
Years ago, Xavier travelled to Tibet to investigate a “mysterious walled city in the shadow of the Himalayas”. He telepathically suggests to the guards to allow him to enter the city gates, sensing also that someone else is controlling the guards. Inside, the enslaved residents of the city tell Xavier that no one is “permitted to gaze upon” the “master” of the “citadel”. Xavier is undeterred by the warning and investigates further. He senses advanced technology inside the citadel and that the “master” is up to no good. He forms a rebellion to take down the citadel’s tyrannical ruler. As the rebels storm the citadel, Xavier strays from the rebels in search of the tyrant. He comes face to face with Lucifer, who crushes Xavier’s legs with a falling slab from the ceiling.
After his encounter with Lucifer, Xavier decides to form the X-Men when the time comes for “mankind to meet the renewed threat of Lucifer”.
Lucifer sets his plan in motion. It is also discovered that Lucifer answers to a superior.
Cyclops, Beast, Angel and Iceman make their way back to the Institute. They find Xavier in his comatose state, and Marvel Girl is the only one able to communicate with Xavier. She relays Xavier’s instructions to Beast to build a “beam distorter”. Once the contraption is ready and put over Xavier’s head, Xavier regains consciousness.
The X-Men waste no time preparing to set off to face Lucifer in the “Southwest Desert” in Xavier’s new private jet. But Marvel Girl senses Cyclops’ attitude towards her has changed from caring to harsh.