Lion-O, who is constantly sneaking out of the palace, is caught up in a fight between a helpless dog and some "alley cats". He decides to step in and help. When it looks like he's outmatched, he's suddenly helped by a stranger, Cheetara. Lion-O shows Cheetara the reason he came to that part of town "technology things" which he buys from a dealer and tries to find out how they work.
Unfortunately, he discovers he's late for a ritual of initiation and leaves. He arrives at the palace late and then undergoes the ritual of being chosen by the Sword of Omens to be the next king of Thundera. He has a vision involving a demonic being with glowing red eyes. Not knowing if anyone will believe what he's seen, he makes up a story and leaves with Tygra.
His father Claudus does not feel Lion-O is ready to be king, being too lenient and easily distracted by flights of fancy and myths of ancient technology. Soon after, King Claudus welcomes the return of General Grune, his old friend. All the people are saddened to learn that General Panthro has fallen in battle.
Claudus holds a celebration in both Grune's honor and in memory of the fallen Panthro. During the event, Lion-O defends a pair of captured Lizards and convinces his father to release them.
- The new series takes place on Third Earth, where the ThunderCats have a thriving kingdom which is called Thundera. In the original series, Thundera was the home world of the ThunderCats, and was destroyed, forcing them to flee in a starship.
- An almost exact look-a-like of the character Lynx-O, from the original series is seen in one of the look-out towers. Though his name isn't spoken in the episode, this look-out is blind and has a heightened sense of smell.
- When Lion-O is looking to purchase black market items that could potentially be technology, he picks up an item that appears to be the paw of a Berbil.
Captured lizard: (to other captured lizard, who pleaded for mercy) Forget it! Looking for mercy from cats is like trying to squeeze water from a stone!
(To Lion-O) We only attack to survive. You control the best lands and resources, leaving the rest of the animals to fight over scraps! If we steal your crops, it is to feed our children!
(To Tygra) Criminal?! The lizards’ only crime is being weaker than the cats! And it's the same for all animals.
- Thundercats.ws :Reminder – Thundercats Airs Tonight "Tonight’s premiere gives us the first two episodes of the show; The Sword of Omens and Ancient Spirits of Evil." (Archived on Internet Archive Wayback Machine on May 06, 2020)