The ThunderCats are busy trying to salvage as much equipment and food rations as they can from the wreck of their fallen spaceship. Panthro, while initially angry that most of their equipment has been destroyed, is confident that enough Thundrillium is left to build a ThunderTank. Lion-O decides to scout the surrounding area, taking the Sword of Omens and Claw Shield with him while Tygra and Cheetara go searching for a suitable location to build Cats Lair.Meanwhile, the Mutants, while searching for the ThunderCats as well as a suitable location to build Castle Plun-Darr, come across an old pyramid. As they approach the pyramid, it starts to emit lightning, forcing the Mutants to land their ship. Inside the pyramid, Mumm-Ra emerges and offers the Mutants a chance to ally with him to obtain the Eye of Thundera. At first the Mutants reject his offer and threaten to blow up Mumm-Ra's pyramid. Mumm-Ra in turn retaliates by sinking their spaceship where it stands. The Mutants, now weaponless without their ship, have no choice but to join forces with him. He teleports them to the woods where Lion-O is scouting alone.The Mutants re-materialize in the woods and ambush Lion-O but he manages to call for help using the Sword of Omens and Panthro, Wilykit and Wilykat arrive to rescue him. Defeated by the ThunderCats, the Mutants teleport back to Mumm-Ra's pyramid. Lion-O, surprised as to why Tygra and Cheetara did not see the Cat signal, goes off in search of them.Back inside the Black Pyramid, Mumm-Ra ridicules the Mutants for failing miserably to obtain the Sword from Lion-O. The Mutants retort by taunting Mumm-Ra which greatly angers him and he decides to show them his true power by transforming into his Ever-living form and flying out of his pyramid.While searching for Tygra and Cheetara, Lion-O comes across a strange black lake which is filled with thick, hot, bubbling black ooze. Mumm-Ra suddenly appears and a fight ensues between him and the young lord. The Sword is knocked from Lion-O's hands and falls into the black lake. Lion-O retrieves it and tries to call the other ThunderCats, but the Eye of Thundera, now covered by the black ooze, does not respond. Mumm-Ra manages to pin down Lion-O and in a desperate attempt to shield himself from the fiend, Lion-O holds up his Claw Shield in defense. Mumm-Ra, upon seeing his reflection in the Claw Shield, is horrified and driven back to his pyramid.