From the introduction: The planet Thundera, famous for its beauty, magic and wealth, has been destroyed. The surviving nobles, called Thundercats, flee on a spaceship, but are hunted by their old enemies the bestial barbarians called Mutants, their fighting causing both ships to crash in the planet named Third Earth. In the Third Earth the Ancient Spirits of Evil have awakened the Mummy sorcerer Mumm-Ra and tasked him with taking the thunderans greatest magical treasure the Sword of Omens.