The inhabitants of the planet Thundera are evacuating just before it is destroyed. They were being pursued by a gang of mutants. All of their escape ships, except for one, were destroyed. Only a small group of Thunderans (Thundercats) remained. With only half of the engine power, the group, led by Jaga, had to set a course for the nearest planet. Jaga commanded their ship while the other seven were in their stasis tubes. Jaga died during their journey to Third Earth, and their ship crashed there. Soon, they made friends with various groups in the area and designed a fortress. Mumm-Ra, the embodiment of evil for centuries, along with the mutants who destroyed the rest of the Thunderans, poses a constant threat. But Lion-O, the new leader of the Thundercats, with his weapon "Sword of Omens," will help the Thundercats have a real chance.