The ThunderCats are on the move! After the kingdom of Thundera is attacked by the lizard people, Lion-O leads Tygra, Cheetara and the other heroes on a quest for the Book of Omens and the magic stones of legend. But he'll have to face villains like Mumm-Ra, the ancient evil sorceror, and Slithe, the dangerous lizard general. Luckily, he has the Sword of Omens and its amazing powers at his disposal.

The inhabitants of the planet Thundera evacuate just before it is destroyed. They were pursued by a band of mutants. All but one of their escape ships was destroyed. Only a small group of Thunderians (Thundercats) remained. With only half engine power, the group, which was 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 on their journey to Third Earth and their ship crashed there. Soon they made friends with various groups in the area and they designed a fortress. Mumm-Ra the centuries-old embodiment of evil, along with the mutants that destroyed the rest of the Thunderians are a constant threat. But Lion-O, the new leader of the Thundercats, with his weapon the "Sword of Omens" will help the Thundercats to have a standing chance.