Inside Cats Lair, Panthro and Tygra are concerned about the multiple earthquakes which are occuring in the area. Tygra goes out to investigate but the ground underneath his feet opens up and he falls down the crack. As he climbs out, he is attacked by a giant worm. The worm drags Tygra with it into the ground.Undeground, Tygra notices a trail of glowing slime left by the worm and starts to follow it. He first encounters twoMolemen who are just as clueless about the quakes as he is. As Tygra continues to chase the worm, he meets Silky, a plant with a human face. She welcomes Tygra to the Garden of Delights and offers him a yellow fruit. Tygra tries to resist but eventually ends up taking a bite out of the fruit. He immediately starts hallucinating and enters a sort of euphoric state where he imagines himself flying.Now that Tygra is addicted to the fruit and completely under its spell, Silky transforms and reveals herself to be Mumm-Ra. The evil mummy gives Tygra another fruit but in exchange he has to steal the Sword of Omens for him.Back outside Cats Lair, Panthro and Wilykat are using the ThunderTank to clear up the fallen trees that were uprooted by the earthquakes. Tygra returns back to the lair, still in a dazed state and almost gets hit by the tank. Panthro gives Wilykat a chance to drive the tank but he is unable to control it and the vehicle plunges down one of the crevices. Thankfully neither of the two are hurt. Lion-O and Cheetara climb down the crevice as well to investigate the network of tunnels created by the giant worm.Meanwhile, Tygra, who is unable to sleep due to Silky's voice echoing in his head, steals the Sword of Omens and delivers it to Mumm-Ra in his pyramid. Knowing that the sword cannot be used by evil, Mumm-Ra summons the Mutants and the two concur that they need to find a "pure spirit" for their scheme to succeed. They set a trap which teleports their chosen "pure spirit", Willa, inside Mumm-Ra's pyramid. Mumm-Ra then tries to tempt the Warrior Maiden with unlimited power if she sides with him. However, the sword's "Sight beyond sight" shows Willa what has transpired so far but she plays along and pretends to crave the power to rule Third Earth.The Warrior Maidens led by Willa attack Panthro and Tygra and tie them up. The Mutants and Mumm-Ra arrive and lock up Lion-O, Cheetara and Panthro in an inescapable room inside Cats Lair. Panthro then resorts to his ingenuity and uses his belt insignia, which is actually a flying recording device. He uses a remote control to guide the device out of the room via the skylight. Outside, the device captures the discussion taking place between Mumm-Ra and Tygra in which, in exchange for another fruit, Tygra reveals that Mumm-Ra will never be fully successful as long as Lion-O lives. Mumm-Ra, realizing that Tygra is right, tells Willa to prepare for battle as he hands the ThunderCat another fruit. Tygra however, only pretends to eat the fruit and Willa is the only one who sees it.Mumm-Ra, Willa, the Mutants and the captive ThunderCats are all transported to some sort of ancient ruins where Mumm-Ra begins to proceed with his sinister plan. However, he is interrupted by Tygra who is now back to his senses. At that point Willa frees Lion-O and throws him the sword. The ThunderCats all spring to action and once again defeat the Mutants and Mumm-Ra.