In a distant galaxy, the world of Thundera is in crisis. The planet's structure has become unstable and is near collapse. With their destruction imminent, Thundera's denizens--known as the Thundercats--escape in a spaceship and plot a course for a new home. While in transit, the Thundercats are attacked by evil mutants and their craft is irreparably damaged. Jaga, the eldest Thundercat, sacrifices himself in order to pilot the ship safely to its destination: Third Earth. Upon reaching the new planet, the Thundercats--Lion-O, Panthro, Cheetara, Tygra, WilyKat, WilyKit and Snarf--must fight evil with the aid of the magic Sword of Omens. From their headquarters known as Cat's Lair, the Thundercats face off against the mutants, who have followed our heroes to Third Earth. It won't be an easy contest, because the mutants have a powerful new leader: Mumm-Ra, the Ever-Living. It's up to Lion-O and the rest of the Thundercats to restore peace to Third Earth.