While fleeing through space to escape their dying home world, the ThunderCats are attacked by their mortal enemies, the Mutants of Plun-Darr, and forced to divert their damaged flagship to a planet called Third Earth. Now, the last survivors of Thundera strive to rebuild their society in harmony with the new world’s natives. But the Mutants, determined to possess the ThunderCats’ mystical gem, the Eye of Thundera, have tracked them down – and they’ve also forged an alliance with the sinister Mumm-Ra, the devil-priest of Third Earth!