Lion-O springs Jaga from the Astral Prison.
We open in the Sword Chamber, where the Eye of Thundera in the mystic Sword of Omens is signalling that a Thundercat is in danger! This wakes Lion-O up, and he rushes in and calls upon the power of sight-beyond-sight. First, he sees an unusual structure in a bizarre, dreamscape-esque location.
We zoom in through one of the windows, and we see that Jaga is restrained against a wall. A three-eyed, four-armed, screechy-voiced blue guy claims responsibility for capturing Jaga, and tells Jaga that he’ll be a prisoner there for all eternity.
Lion-O runs off to consult with the other Thundercats. We cut to Mumm-Ra’s pyramid, where Mumm-Ra emerges from his sarcophagus to investigate unusual activity he has detected at Cat’s Lair. He uses his cauldron to spy on the Thundercats as they meet in their council chamber to talk about the whole “Jaga imprisoned for all eternity” thing.
The Thundercats figure that in order to save Jaga, they’ll need to find somebody who knows a lot about the “Astral World”. Wilykat explains that there’s only one person like that on Third Earth, and Wilykit provides us with her name: The Nether-Witch. Where did they learn that? Maybe they swiped Roberbil’s rolodex or something. Regardless, Mumm-Ra is pretty stoked about this turn of events, since there’s a little fact about the Nether-Witch that Wilykit and Kat don’t know: the Nether-Witch and Mumm-Ra are one and the same!
“Ancient Spirits of Evil, transform this decayed form to Mumm-Ra the Ever-living!” Once’s he’s been suitably transformed, he busts out with, “and now, Sorcerors of the Netherwold, make Mumm-Ra the Nether-Witch!”
Back at Cat’s Lair, the Thundercats set out in the Thundertank. Panthro nearly drives the tank into a chasm, which alarms Lion-O, but Panthro merely extends the front paws to grab the other side of the chasm to pull them across (I guess Panthro made some chasm-crossing enhancements to the tank since he very nearly botched the same maneuver back in episode 19).
The tank pulls up at what Panthro helpfully identifies as the Bridge of Slime. The Pit of the Nether-Witch is on the other side. Can you imagine how hard the realtor must have been working to sell that property to her? “Well, it’s a pit, and it’s only accessible via a bridge of slime, but the schools in this neighborhood are terrific!”
Tygra offers to come with Lion-O, but Lion-O inexplicably decides that he has to do it alone. The other Thundercats zoom away. Using the Claw Shield to stabilize himself, Lion-O begins to climb over the slimy bridge. When he’s at the midway point, a two-headed monster with very long necks pops out of the water under the bridge to menace him. He tries to pull his sword to deal with the heads, but loses his footing on the slippery bridge and slides off the side. He manages to jam the Sword of Omens into the bridge to create a handhold, and the monster menaces him some more.
He jumps back up on top of the bridge, the monster gets bored and sinks back into the river underneath, and Lion-O finishes crossing the bridge without further incident.
We cut to Castle Plun-Darr, where Slythe, Jackalman, Monkian, and Vultureman are putting the finishing touches on a Thundrainium Cannon. Mumm-Ra has apparently told them that Lion-O will be out of the way, so they think this will be the perfect time to get rid of the rest of the Thundercats.
We cut back to the Pit of the Nether-Witch. Lion-O heads inside, and is accosted by a spooky translucent eyeball. And a spooky translucent hand. And some spooky translucent faces.
Eventually, he is attacked by a dinosaur with a spiky nose and three glowing eyestalks.
He tries to back away from the dinosaur, but falls down into a chasm in the process, getting knocked unconscious at the bottom. When he wakes up, he meets the Nether-Witch. She makes a big deal out of already knowing who he is and what he wants, kind of like a website that tries to personalize its content for you.
Lion-O asks to be transported to the Astral World. The Nether-Witch warns him that once he’s there, he’ll never return. Lion-O says “but”, and she screams at him, “NO, YOU WILL LEAVE THIRD-EARTH FOREVER!!!!!” Then she calms down again and tells him that it’s up to him. Don’t you just hate those high-pressure salespeople? Lion-O says he’ll do anything to free Jaga, so the Nether-Witch begins her spell. “Ancient Spirits of the Void, transport Lion-O to your Astral World!”. In the process, she reverse-transforms into Mumm-Ra.
Lion-O materializes in the Astral World, near the prison building we saw earlier. “Time to find out if my powers work in this Astral World.” Apparently he’s talking about his awesome power of “swinging on a rope.” He shoots one of the claws of the Claw Shield, trailing a line, up to the roof of the Astral Prison and swings across to it.
He begins to climb up, but the Eye of Thundera alerts him to some danger. He looks down, and sees that a big monster is jumping at him out of the water that surrounds the prison.
He tries to climb away from it, but as he’s jumping around to dodge the thing he knocks the claw loose from where it had been secured on the roof and begins to fall. The claw snags itself on another ledge, and he’s able to dodge the creature again. The monster, fed up with Lion-O dodging whenever it leaps, decides to just climb up the wall after Lion-O. Lion-O draws his sword. “HO!” He zaps the monster with a sword-beam. The monster shrugs off the first attack, so he has to zap it again before it falls off the wall back into the water.
We cut to Castle Plun-Darr where the Mutants are ready to head out. Slythe asks Vultureman if the Thundrainium Cannon is ready. Vultureman answers in the affirmative. He then also adds that it’s loaded with Thundrainium shells, the only material on Third-Earth that’s known to weaken the Thundercats. I would have thought that was sort of implied by its very nature as a Thundrainium Cannon. They head off towards Cat’s Lair, Slythe on the nose-diver, Jackalman and Monkian on skycutters, and Vultureman driving the Thundrainium Cannon.
We cut back to the Astral Prison, where the three-eyed guy is explaining that he’ll consider freeing Jaga if Jaga surrenders all his knowledge to the three-eyed guy. Jaga thinks that will happen… never!
“Brave words, feeble fool, but I, Nevex, have all eternity to change your mind. And, Jaga, you can be sure I will change your mind!” Lion-O chooses this dramatic moment to burst in through the door. Nevex does something magical and becomes taller and more muscular. He also starts trying to zap Lion-O with beams from his eyes and hands.
Jaga tells Lion-O to use the Eye of Thundera. Lion-O whips out the sword and intercepts Nevex’s beams on the Eye, and then beams from the Eye push back and zap Nevex.
Nevex is returned to his scrawny form and collapses. Lion-O rips Jaga’s metal restraints from the walls, freeing him. He notices that Nevex is waking up, so he hustles Jaga out of the room, shuts the door behind him, and welds it shut with more beams from the sword.
As they run through the prison, they hear someone in one of the cells calling for help. Jaga tries to open the door, but Lion-O makes him stand aside so he can do it. Inside they meet a little old man with a long white beard. He claims to be Brodo. Many centuries ago, Brodo was the most powerful magician on Third Earth, but his wizardry threatened Mumm-Ra’s evil dominion, so Mumm-Ra tricked him, and he’s been locked in the Astral Prison ever since.
Lion-O picks the guy up, bride-and-groom style, and takes him outside. He wants them all to get away before Nevex rallies his forces. He shoots a line from his Claw Shield across the moat, and they all swing to safety.
Jaga is happy to see Lion-O, and Lion-O explains that since going to the Astral World is a one-way trip they’ll be together forever. Just then, the Eye of Thundera alerts them to Thundercats in danger, so Lion-O uses sight-beyond-sight to see that the Mutants are attacking Cat’s Lair!
Inside the lair, the Thundercats realize the Mutants are using Thundrainium. The Thundrainium level is at 129, and rising! Panthro identifies the cannon as the big problem, and takes the Thundertank out to deal with it. Vultureman, however, nails the Thundertank with his cannon and flips it. Panthro is forced to flee, with Jackalman strafing him in a skycutter.
We cut back to Lion-O, who is starting to regret his decision to make a one-way trip to an alternate dimension. Brodo, by the most amazing coincidence, has the power to send Lion-O back. “Ancient Spirits of Good, transport this young Lion-O back to his own world!”
We cut back to Cat’s Lair, where Panthro is still dodging fire from a skycutter as he runs back toward the relative safety of the lair. Inside, Cheetara and Tygra are trying to use some laser-cannons to take out the skycutters, but they can’t hit him. Then, everyone hears a disembodied voice: “Thunder, thunder, thunder, Thundercats, HO!” Lion-O materializes, in gigantic translucent form, in front of the lair.
He zaps the Thundrainium Cannon with beams from his giant sword, blasting Vultureman clear and destroying the cannon.
He shrinks down to his normal size and becomes solid, and the Thundercats that were inside charge out of the main entrance of the lair behind him, and Panthro runs up to join them.
The Mutants start to flee. Cheetara chases after Jackalman and throws her stick at his skycutter, damaging it (keep in mind this was the same skycutter she wasn’t able to hit with a laser cannon). Lion-O chases down Vultureman and zaps him with his sword. Vultureman cartoonishly runs away, dodging more blasts from Lion-O.
Tygra extends his flaming bolo whip out to hit Monkian’s skycutter, even though Monkian seems to have some pretty good altitude. Monkian loses control and crashes in some woods. Panthro chases after Slythe in the nose-diver on foot (remember that the nose-diver was appreciably faster than the Thundertank back in episode 14, so Panthro must really be booking). He tosses his nunchucks and damages the nose-diver, sending it off-course and right into the line of fire of Wilykit and Wilykat, who throw exploding pellets at it.
Slythe crashes the damaged nose-diver into a hill, and then drives away. The Thundercats all gather in front of the lair for a resounding “Thundercats HO!”, and then all have a good laugh about it.
In the coda, Jaga’s ghost shows up to thank Lion-O for rescuing him. Lion-O says it wasn’t any more than Jaga did for them when he saved the Thundercats and sent them to Third Earth. Jaga has a good laugh and acknowledges that this makes them even. Jaga doesn’t mention that he’s grateful that he doesn’t have to spend eternity hanging out with Lion-O 24/7, but I think you can see it in his eyes.