The Thundercats capture the Lunatacs, put them on trial, and exile them to a desolate planet. However, there is another old enemy of the Thundercats trapped on Exile Isle, with whom the Lunatacs soon team up to plan a destructive return to Third Earth.

Key to Thundera

During an attempt to decode the Book of Omens, Lion-O accidentally traps himself within its pages, prompting Mumm-Ra to try to steal the book from Cats' Lair. Meanwhile, Panthro discovers a mysterious key on New Thundera.

Return of the ThunderCubs

Tygra, Cheetara and Panthro fall under Mumm-Ra's power on New Thundera, and he tries to use Cheetara's Sixth Sense to locate the Treasure of Thundera. To rescue his friends, Lion-O must convince the mutants to fly him from Third Earth in the Ratstar.

The Formula

Alluro's new superfuel formula for Sky Tomb unexpectedly seems to boost the growth of local plant and animal life to massive proportions. Luna orders the mutants to spray it around Cats' Lair, leaving the Thundercats trapped in a gigantic savage garden.

Locket of Lies

Mumm-Ra creates an evil trinket which the Thundercats mistake for a piece of the Treasure of Thundera. It soon leads them into deep trouble on New Thundera, and nobody is around to rescue them.

Bracelet of Power

The Feliner returns from New Thundera with a mysterious bracelet. When Snarf puts it on, he discovers it has the power to turn Thundercats into his obedient servants. While he toys with this new power, Mumm-Ra plots to steal the bracelet for his own evil purposes.