While Don, Professor Robinson, the Robot, and Will are away from camp on a scientific expedition, two aliens, each a warrior champion representing their planet, land near the Robinson camp and begin preparations for individual combat to resolve a conflict between their races. One is a disagreeable frog-headed creature and the other is a handsome, golden skinned human. Penny befriends the frog-headed alien who is adamant about being left alone. The golden alien appears generous to Dr. Smith, Penny, Judy, and Maureen, even apparently saving Judy from an explosive trap, convincing Dr. Smith to hand over to him the Robinsons' weapons against which the frog creature has no defense. Penny has been slowly winning over the frog creature, although he still is hesitant about being friendly in return