Inside the Black Pyramid, Mumm-Ra summons the Driller and instructs him to kidnap Panthro and bring him to his pyramid in exchange for diamonds. Leaving the pyramid, the Driller burrows underground into the Cats Lair. He surfaces inside Panthro's room where the ThunderCat is sleeping. Panthro awakes and the two engage in a short struggle before the Driller drugs Panthro using "Sands of Sleep" causing him to lose consciousness and then drags him underground with him.
The Driller delivers Panthro to Mumm-Ra, collects the remaining half of his diamonds, and leaves the pyramid. Mumm-Ra sets the unconscious Panthro on his Cloning machine and activates it to create a mold of the ThunderCat. He then levitates Panthro and fills the empty mold with a gas which solidifies into an exact replica of Panthro. Mumm-Ra summons the spirit of Hammerhand from the depth of the seas to inhabit his clone body and bring it to life. The evil mummy instructs his creation to terrorize the inhabitants of Third Earth and the clone sets off to bring this task to fruition.
Mumm-Ra transforms into his ever-living form and flies out of his pyramid, carrying the real Panthro with him. Panthro regains consciousness just before Mumm-Ra drops him into the Bottomless Chasm. Luckily, Panthro lands on a ledge deep within the chasm. He starts to climb out of the abyss using his shoulder spikes but is careful to avoid the high intensity Cosmic rays that the chasm emits every thirty seconds.
Back at a Cats Lair, the Sword of Omens warns Lion-O that Panthro is in danger and its "Sight beyond sight" shows him being carried by Mumm-Ra but before Lion-O can see the location, the vision is disrupted by the Cosmic radiation. At that moment, the control room's screen shows the Berbils' fruit fields on fire. Lion-O dispatches Tygra and Cheetara to help the Berbils and he sets off to find Panthro in the ThunderTank. Lion-O eventually arrives at the Bottomless Chasm just as Panthro barely manages to climb out of it. As Lion-O is helping the exhausted Panthro into the tank, he receives a message from Cheetara that the Wolos were being attacked and Lion-O heads for the Wolo Village.
As he arrives at the village, the Wolo Traveller is shocked to see Panthro and claims that the ThuderCat was the one responsible for all the destruction. Lion-O suspects that perhaps Panthro had done so under the influence of the drug that the Driller gave him. But Panthro is adamant that he is innocent. Lion-O tells Panthro to take the tank to the lair while he sorted out the matter.
A short while later, the Wolo runs up to Lion-O and informs him that Panthro had returned and was destroying their village. Lion-O quickly reaches the scene and is shocked to see Panthro wreaking havoc. Thinking that his friend may be under some sort of evil influence, he calls the other ThunderCats, hoping that all of them together may be able to subdue Panthro without hurting him.
Suddenly the real Panthro arrives in the ThunderTank and the two engage in combat. Lion-O wants to help but is unable to tell the real Panthro from the fake. Snarf then suggests that he use the sword as it would only harm the fake Panthro. Lion-O does so and the sword badly burns the clone and he flees from the scene.
The clone Panthro arrives at Mumm-Ra's pyramid, furious that Mumm-Ra did not give him enough power to fight the ThunderCats. Mumm-Ra blames the clone for the failure and tells him that he has no use for him anymore. Mumm-Ra says that with his mold, he can make as many clones as he wishes. The enraged clone lifts the mold and smashes it. He then reverts to his true form of Hammerhand and leaves.