Mumm-Ra has a new device, the Babylonian Barbarian Boiler, that he plans to use on Cats Lair. Ma-Mutt fools around too much and Mumm-Ra banishes him from the Pyramid. Later, the Thunderkittens, Snarf, and Snarfer bring Ma-Mutt back to Cats Lair and then Mumm-Ra fires the Boiler's beam at the Lair, which causes it to start melting. Snarfer makes a communicating device (because Ma-Mutt was trying to tell them about the beam), so they can understand Ma-Mutt. Ma-Mutt starts telling them of the Boiler, but Mumm-Ra sees this and through the Cauldron's magic brings Ma-Mutt back to the Pyramid. Then the ThunderCats construct a giant Light-Shield and use it to protect the Lair, but Mumm-Ra just boosts the power on the Boiler, destroying the Shield. Lion-O uses the Cat Signal to push back the beam, which causes the Boiler to explode, and the Signal restores Cats Lair. Mumm-Ra, who was lonely without Ma-Mutt, welcomes his dog back to the pyramid
