A spaceship approaches third Earth and it sets off all the alarms of the ThunderCats, Mutants and even Mumm-Ra.  It contains enough radioactive material to put an end to the ThunderCats.  Jackelman takes the recovered materials first and Mumm-Ra takes it from him.  The ThunderCats battle Mumm-Ra on top of the Dark Pyramid for the sphere and eventually win, setting the materials to explode safely in space.
               
              
                Casts: 
                Bob McFadden, Larry Kenney, Earl Hammond, Lynne Lipton, Earle Hyman, Peter Newman, Gerrianne Raphael, Doug Preis