The Sword of Omens & Ancient Spirits of Evil Part 1.Lion-O, who is constantly being outdone by his adoptive older brother Tygra, undergoes the ritual of being chosen by the Sword of Omens to be the next king of Thundera. Soon after, King Claudus welcomes the return of his friend Grune and holds a celebration in both his honor and in memory of the fallen Panthro. But during the event, Lion-O defends a pair of captured Reptillians and convinces his father to release them. The next day, Thundera is attacked by Reptilians who have acquired salvaged technology. It is soon discovered that this was organized by Grune and that Panthro is being held hostage. Though Lion-O comes to his father's aid, "Panthro" is revealed to be Mumm-Ra, an old nemesis of the Thundercats, who murders the king while Lion-O and Tygra are captured along with Jaga and Cheetara. However, due to his kindess to the Reptilian prisoners, Lion-O manages to escape with Tygra as they rescue Jaga and Cheetara, with Lion-O grabbing the sword to blast Mumm-Ra out into open as the rising sun's rays harm him. Forced to leave Jaga as he sacrifices himself to ensure their escape, Lion-O, Tygra, and Cheetara undergo a quest to find the Book of Omens along with Wilykit & Wilykat.