The inhabitants of the planet Thundera evacuate just before it is destroyed and are immediately pursued by a band of mutants. All but one of the escape ships is destroyed. Only a small group of Thundercats remain. With only half engine power, the group sets a course for the nearest planet. Jaga commands the ship while the others are their stasis tubes. Jaga dies and their ship crashes on Third Earth. Soon they make friends with various groups in the area and they design a fortress. Lion-O, the new leader of the Thundercats will help the Thundercats stand a chance.