Thundercats: Mumm-Ra tries to get away but the Sword of Omens breaks open the casket dropping the treasure all over the planet, and Snarf, Snarfer, and one other snarf escape. Mumm-Ra gives a false Book of Omens to Ma-Mutt, Slithe and Vultureman, who have arrived on New Thundera in the Rat-star, for safe keeping so that he can decipher the real Book of Omens. The Thundercats go after them through the Caverns of Cold. They head toward the Canyons of Youth, but due to the effects of the canyon, Panthro, Cheetara, Tygra, Snarf, and Snarfer are changed into Thundercubs. Lion-O must use the sword to give the Thundercubs Thundercat understanding. Meanwhile on Third Earth, Jackalman, Monkian, and the Lunataks attack Cats Lair and capture Ben-Gali and Wilykit. Lion-O learns that the Thundercats back on Third Earth are being held prisoner in Sky Tomb, so he decides to send the Thundercubs to Third Earth to rescue them while he tries to get the Book of Omens from Mumm-Ra. Snarf decides to stay with Lion-O and the other Thundercubs prepare the Feliner to leave New Thundera but Mumm-Ra arrives and attacks the Thundercubs.