Before the X-Men can locate Xavier, they need to fix Cerebro first. Angel and Iceman are idle while Beast and Cyclops repair Cerebro. Cyclops orders Angel and Iceman to “turn in” because they “can’t be of any help”. Angel is upset that Cyclops thinks he and Iceman “can’t pull [their] weight”. Cyclops further explains that he merely does not want “all five of [them] bleary-eyed if Factor Three decides to attack again”. Later, he goes to apologise to Angel for lashing out at him because he was exhausted. With the misunderstanding cleared up, Marvel Girl returns to Metro College.
When Jean returns to her room at Metro College, her room mate Carole informs her that she missed a call from Ted that was “urgent”. Ted tells Jean that his brother Ralph is “captured” and he needs the X-Men’s help. Jean asks Ted why he thinks she “can reach the X-Men” but he hangs up before she can get an answer. She strongly suspects Ted knows she is Marvel Girl.
Marvel Girl calls the Institute. Angel and Iceman answer her call and go to fetch Marvel Girl. They did not inform Cyclops and Beast because Cerebro needed to be repaired. Marvel Girl, Angel and Iceman meet Ted at Roberts Research labs. Ted tells them that Ralph had been “taken as a prisoner to the centre of the earth” by “Tyrannus”, “the ruler of a world beneath the earth”.
Ralph had discovered a cobalt alloy so strong it could possibly penetrate the earth’s core. Then “Tyrannus” came from beneath the earth to take enslave Ralph. Ted was knocked unconscious while Ralph disappeared into the earth. Ted shows the X-Men their “atomic powered earth-borer--fitted with plates of Ralph’s new super-cobalt. This vehicle should be able to allow the X-Men to follow Tyrannus into the earth. After plunging down the fifty-foot chasm, the X-Men stumble upon a huge cavern. But instead of finding Tyrannus, they come across the “Mole Man”.
Angel pummels the Mole Man, who calls for his backup “BEM’s”. The slow-witted BEM⁏s are no match for the X-Men. They chase the Mole Man deeper into the caverns. Then, they encounter a strange mist that causes amnesia.
Meanwhile, Ralph is forced to work on coating Tyrannus’ giant robot with his cobalt alloy. Tyrannus wants to defeat his rival, Mole Man’s “giant robot of solid diamond”.
Cyclops and Beast found out where Angel and Iceman were headed, and enter the cavern.
Marvel Girl, Angel and Iceman have lost their memories. The Mole Man takes them to his lair to see his robot. He convinces them that Tyrannus is their mutual enemy, and they should fight Tyrannus for him.
Cyclops and Beast find Roberts Research’s earth-borer. They decide to use the vehicle as transport.
The Mole Man sends his diamond robot to attack Tyrannus, who in turn sends out his cobalt alloy robot. With the help of the X-Men, the Mole Man’s robot defeats Tyrannus’s robot. Outraged that his robot was so easily defeated, Tyrannus discovers that Ralph had added a “low heat resistance” substance into the cobalt alloy.
Marvel Girl, Angel and Iceman infiltrate Tyrannus’ lair and intend to capture him.
At the same time, Cyclops and Beast infiltrate the Mole Man’s lair and take him hostage. They demand that the Mole Man take them to other X-Men.
Angel attacks Cyclops at first sight. Cyclops refrains from using his optic blast on Angel, and settles for bumping him on his head. This relieves Angel of his amnesia. Soon after, Marvel Girl and Iceman are cured as well. Tyrannus surrenders to the X-Men.
The X-Men subject Tyrannus and the Mole Man to the mist that causes amnesia. They return to the surface with Ralph.
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