The Thundercats have been out hunting all day, with no luck. After a near miss, everyone except Panthro, give up and start to head home. Just then they are ambushed by mutants. Meanwhile, Panthro stumbles upon an ancient Si-Tare graveyard, and is attacked by the spirit of their leader, Ashtar. He manages to destroy a tombstone, which temporarily vanquishes Ashtar, and runs for his life. Back at the battle between the Thundercats and the mutants, Wilykit and Wilykat use paralysis powder to disable the mutants, so everyone can flee. They suddenly find themselves in a strange fog, which fills their very beings, but just as quickly as it appeared, it disappears. They dismiss the strange event, and continue home, meeting up with Panthro on the way, who doesn't mention what happened to him.
That night all the Thundercats, except Panthro, become feverish and delirious. Panthro hears the voice of Ashtar, telling him he is being punished for destroying the tombstone, so he decides to head back to the graveyard to try and save his friends. Meanwhile, a mutant who had been spying through the window, returns with reinforcements, so they can take out the Thundercats while they are unwell. The threat of battle wakes the Thundercats from their delirium, and they defeat the mutants. Cheetarah remembers hearing Panthro say he was headed to the graveyard, so they go after him.
At the graveyard, Panthro confronts Ashtar, and demands he take a solid form, so they can fight. Panthro is no match for Ashtar, but just in time the Thundercats arrive. Lion-o uses the Sword of Omens to call down lighting, sending the spirits back into their graves. Knowing the whole incident was partly his fault, Panthro repairs the tombstone he destroyed.

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