Other issues:
Professor X is missing, and Cyclops and Beast are attempting to repair Cerebro. There's nothing for the other X-Men to do, so they decide to get some rest while Jean returns to college.
Jean receives a call from Ted Roberts, warning her that his brother Ralph had been captured and that she must call the X-Men to help him. Jean thinks he knows about her secret identity, but still calls the others and tells the story. Angel and Iceman get the plane, catch Marvel Girl and go find Ralph. Ted tells them that a man called Tyrannus kidnapped his brother because of his work with cobalt and took him to the core of the Earth. The X-Men then use Ralph's new vehicle, made of cobalt, and go after Tyranus. When they reach Subterranea, they find a strange man. It's not Tyrannus but Mole Man, his archenemy, and he attacks the X-Men. Mole Man leads the three X-Men towards the River Lethe where they forget who they are and become his servants.
Meanwhile, Ralph is finishing his work with Tyrannus, constructing a giant cobalt robot to fight against the giant diamond android made by the Mole Man. After Cyclops and Beast had noticed their missing fellows, they followed them into the caves with the help of Cerebro. Later, the two giant androids meet and start a battle, which ends with Tyrannus' Cobalt one destroying Mole Man's diamond android. Angel then helps destroy the Cobalt android as well because Ralph Roberts sabotaged his alloy. Tyrannus realizes this and is about to kill Ralph, when Angel, Iceman and Marvel Girl attack and save him. Cyclops and Beast also arrive and attack Mole Man, as Angel tries to stop them because he is still under mental command of Mole Man. Then Cyclops uses an antidote ray on him and the rest of the X-Men to restore their memories. They X-Men return to the surface, leaving the defeated Tyrannus and Mole Man inside the underground cave, after having their own memories wiped by the River Lethe.