Lion-O takes up mountain climbing, but during one of his climbs, theMutants attack him with a Thundrainium gun. Lion-O calls the other ThunderCats, but an avalanche traps Panthro, Tygra, Slithe, andMonkian in a cave causing a limited air supply. MeanwhileJackalman steals the Sword of Omens, but Lion-O manages to get it back and save everyone.