Vultureman escapes from exile by hijacking a bookmobile. He finds a disk containing ancient history about two powerful evil forces on Third Earth: Mumm-Ra and his enemy Zaxx. Using this information, Vultureman plots to defeat Mumm-Ra and rule the universe.

Well of Doubt

The Thundercats use a new Tower signal to guide a Thunderian ship in; aboard are Baron Tass and Mr. Grubber, a devious pair of Thunderians. Later Lion-O sends Torr, Baron Tass and Mr. Grubber to get water, but on the way the Baron stops at the Well of Doubt and gets some of its water. The water causes a person to become very doubtful of his own abilities. When they get back to the Thundercats, Baron Tass gives some of the water to Lion-O. On the way to inspecting the new Tower in the Whisker, Lion-O feels the effects of the water and causes the Whisker to crash. Tass comes back (from getting his Guardsman, giant stone-men), and has them attack the Thundercats. Will Lion-O recover his courage and determination?

The Book of Omens

Finally Panthr-O deciphers how to use the Key of Omens. He enters the code to open the lock and, suddenly, the Guardian of Omens is summoned and it tells the Thundercats they have 24 hours to present both the key and present four other items to the four places in disgrace (geological disasters) all over New Thundera. All was proceeding correctly except for the key, which was stolen by the evil Mumm-Ra. However, he enters the Book just when Lion-O found him and the battle will go on inside the book.