After discovering that the Book of Omens pages are blank, the ThunderCats attempt to figure out the purpose of the mysterious artifact, soon Lion-O accidentally manages to activate the book, and his spirit is transported within the book, where he encounters Jaga who says that Lion-O must relive his ancestor Leo's past to understand what he must do in the present to defeat Mumm-Ra.
Lion-O (in Leo's body) is shocked to learn that the Cats once served as Mumm-Ra's army, and helped him oppress and enslave the other animal people and that Lion-O's ancestor Leo himself was Mumm-Ra's 2nd in command, and that they were transporting slaves to Third Earth aboard the Black Pyramid to toil as laborers and serve Mumm-Ra's armies in recovering an artifact known as the War Stone. Soon with the stone having been located, Mumm-Ra contacts and sends another cat named Tygus to retrieve it.
Lion-O (in Leo's body) soon finds his way to the prison area where Mumm-Ra keeps the enslaved animal people and meets Panthera, another Thunderian seemingly in the service of Mumm-Ra, soon a prisoner revolt breaks out under the leadership of a lizardman named Rezard and a Jackalman named Shen.
The Thunderian guards, Leo/Lion-O and Panthera put a quick end to the riot, and Panthera instructs the guards to take Rezard and Shen into isolation where she and Leo will deal with them personally.
In the small room Panthera frees the pair from their shackles, and Lion-O learns his ancestor is a freedom fighter opposing Mumm-Ra from the inside. Panthera, Leo, Rezard, and Shen make their plans for the battle to come against Mumm-Ra, and the Jackal and Lizard are returned to their cells to organize their people when the time was right to attack.
Returning to the bridge of the Black Pyramid, Leo/Lion-O and Mumm-Ra watch the invasion of Third Earth, Mumm-Ra mentions that he trusts the cats because they, and especially Leo, are just as hated by the animal people as he himself, if not more so. The warstone is soon announced to have been secured and Tygus is returning to the Black Pyramid with it in hand.
While Tygus is en route the Black Pyramid, Leo/Lion-O meets with Panthera and a group of Thunderian blacksmiths who have forged a weapon that can oppose Mumm-Ra and can never be wielded against the forces of good, the Sword of Omens and it's sheath, as well as a powerful weapon in it's own right the Gauntlet of Omens (which Lion-O had thought until now to not be very important)
Lion-O soon meets Tygus who gives him the War Stone, Tygus is then informed of the rebellion, Tygus has little faith Leo will succeed in defeating Mumm-Ra, but does nothing to stand in his way or alert Mumm-Ra to the treason either. Leo/Lion-O places the War Stone in the center of the sword, where it changes shape and becomes the Eye of Thundera.
Leo/Lion-O then confronts Mumm-Ra, who is not phased by the treachery, or intimidated by the Sword of Omens and War Stone, revealing (and pointing out how short Leo's memory must be that he forgot) that he has three other power stones in his immediate possession.
A battle soon ensues and Leo/Lion-O manages to separate the Spirit Stone from Mumm-Ra's gauntlet, Using the power of the remaining two stones, Mumm-Ra is surrounded by magic armor, but due to the War Stone's power, Leo/Lion-O is briefly able to overpower Mumm-Ra and signals the other animals that it is now time to rebel against the oppression of Mumm-Ra.
His foe quickly recovers, but taking a page from Mumm-Ra, Lion-O/Leo takes the Spirit Stone and joins it with his gauntlet and is also surrounded in a suit of mystical armor and defeats the evil being, taking possession of the other two stones of power as well.
The battle has extensively damaged the Black Pyramid and it is now doomed to crash land on Third Earth.
Mumm-Ra, now shriveled small and weak manages to get into his preservation tomb and seal himself within before Leo or Panthera have time to react. But Panthera makes sure that Mumm-Ra can not leave his tomb on his own terms, and destroys the controls that allow it to be opened from the inside.
Leo instructs all aboard to brace for impact. As the ship crashes Leo and Panthera kiss and embrace one another, perhaps for the last time.
Lion-O is returned to the astral plane where Jaga tells him that the crash damaged much of the Book of Omens memory of the exact location of the other three stones is lost, but it can still guide him to them. Jaga also states the stones will not be enough to stop Mumm-Ra.
Lion-O is returned to his body and wakes up with the other Thundercats standing over him, he informs them that they have a new mission: To unite all the animal people together and stand against Mumm-Ra with them.
Keep an eye peeled for characters from two late 1980's animated series: Silverhawks villain Mon*Star, and the title heroes of the show Tigersharks. Both the Silverhawks and Tigersharks were made by the creators of the Thundercats. Mon*Star has slightly been modified to resemble a Thunderian.
|Wilykat ( x ) ( x ) ( x )||
|Wilykit ( x ) ( x ) ( x )||
|Cheetara ( x ) ( x ) ( x )||
|Lion-O ( x ) ( x ) ( x )||
|Tygra ( x ) ( x ) ( x )||
|Panthro ( x ) ( x ) ( x )||
|Snarf ( x ) ( x ) ( x )||
|Jaga ( x ) ( x ) ( x )||
|Mumm-Ra ( x ) ( x ) ( x )||
|Tygus ( x ) ( x ) ( x )||
|Leo ( x ) ( x ) ( x )||
|Panthera ( x ) ( x ) ( x )||
|Rezard ( x ) ( x ) ( x )||
|Shen ( x ) ( x ) ( x )||