Meanwhile on Third Earth, Jackalman, Monkian, and the Lunataks attack Cats Lair and capture Ben-Gali and Wilykit. Lion-O must use the sword to give the Thundercubs Thundercat understanding. 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. The Thundercats go after them through the Caverns of Cold.

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. 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.