The X-Men a reeling from the kidnapping of Professor X, which confirms to the team the seriousness the threat of Factor Three means to the group. As the Beast repairs Cerebro (which was damaged in the kidnapping), Cyclops pulls rank to get his fellow teammates to get their heads together while they figure out how to find the Professor. In the meantime, he orders them to rest and relax, but to be ready for action when they are needed. With this, Jean returns to her dorm room at Metro College.
Arriving at the college, Jean learns that Ted Roberts had called for her in her absence and that he needed to speak with her urgently. Knowing that Ted suspects that she is Marvel Girl of the X-Men, Jean places a call to him right away. Calling Ted, she learns that he is at his brother's research lab and that someone has captured his brother Ralph. He begs her to contact the X-Men and get them to help before abruptly hanging up. Jean contacts her comrades, when Warren takes the call he wakes Bobby up and the two leave to join Jean on their own, not wanting to disturb Hank and Scott's progress in repairing Cerebro.

They pick up Jean in the X-Plane and they soon arrive at Roberts Research Inc. Ted lets them into the factory. Once inside, Ted tells the X-Men that his brother Ralph had been captured by beings from beneath the Earth. He explains that his brother Ralph had just perfected a new Cobalt based metal alloy that is impervious to damage, when suddenly his lab was invaded by Tyrannus and his Tyranoid's who had come to kidnap Ralph and exploit his expertise with Cobalt science. Both Ralph and Ted were easily overpowered and Tyrannus escaped with Ralph as his captive. When the X-Men agree to help, Ted takes them to another invention of Ralph's, an earth borer that is equipped with a Cobalt power source. With the device only fitting three, the X-Men convince Ted to stay behind while they search for Ralph in the cavern below.
Learning the controls, Angel pilots the device down the tunnel dug by Tyrannus and his minions and they find themselves in a subterranean tunnel. Upon their arrival, they are instantly attacked by the Mole Man, who is armed with a disintegration ray. When the three mutants prove too powerful for the Mole Man to tackle alone, he calls his Moloids to deal with them while he flees the scene. The X-Men make short work of the Moloids and follow after Mole Man to learn if he has any connection with Tyrannus. This is playing into the Mole Man's hands, as he leads them to the River Lethe, which unleashes a gas that causes the three X-Men to be struck with amnesia.
Meanwhile, in the home of Tyrannus, the underground dictator has forced Ralph to create a gigantic warrior robot out of his Super Cobalt alloy so that Tyrannus can use the robot against his foes. As Ralph is putting the final touches on this robot, Cyclops and Beast begin scaling the tunnel down to the underground caverns that is home to both the Mole Man and Tyrannus to search for their comrades. They find the Earth borer and use it to travel through the tunnels (thereby safe from the gas from the River Lethe). The Mole Man has convinced Angel, Iceman and Marvel Girl that they are his slaves. Taking them to his lab, the Mole Man reveals that he has been building a robot of his own which he hopes to use against his foe Tyrannus, and also convinces the forgetful X-Men to fight on his behalf.
Back at Tyrannus' lair, Tyrannus is preparing to mount his attack against the Mole Man, but takes a moment to first drink from the Fountain of Youth to maintain his youth and vigor. Just then, the Mole Man's robot attacks his castle, prompting him to order Ralph to unleash the Super-Cobalt warrior that was constructed for him. Tyrannus' robot defeats Mole Man's creation and then Marvel Girl, Angel and Iceman attack the Super-Cobalt robot, easily destroying it. This surprises Tyrannus, who doesn't understand how the robot could easily be defeated, unaware that Ra

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