The Slaves of Castle Plun-Darr is the third episode of the ThunderCats original series. Note, the episode was released as a home release movie Exodus, the Movie, also including episodes: "Exodus", "The Unholy Alliance", and "Berbils"; with some alterations to the episodes.
The Mutants have enslaved a race of creatures known as Brutemen to build them their fortress, Castle Plun-Darr. The ThunderCats set off to help free the creatures but the Mutants have a trick up their sleeve to thwart the Cats' effort.
WilyKit and WilyKat are playing in the forest when they discover that the Mutants have enslaved a race of primitive beings whom they refer to as Brute-men and are forcing them to build Castle Plun-Darr. The Mutants are extremely cruel in their treatment of the Brute-men and beat them severely if they falter. Before the Thunderkittens can do anything, they are spotted by Monkian who chases them but they manage to give him the slip.
Meanwhile, construction of the Cats Lair is proceeding very well thanks to the efforts of the Berbils. Wilykit and Wilykat arrive at the lair and report the Mutants' actions to the rest of ThunderCats. Ro-Bear-Bill, who is also present there, further informs the Cats that the Brute-men are gentle beings who lack much intelligence. The ThunderCats, led by Lion-O, set-off to rescue the Brute-men in the ThunderTank, leaving Kit and Kat to guard the Lair.
The ThunderCats arrive at Castle Plun-Darr and the ThunderTank breaks through the surrounding barricade with ease. Lion-O enters the Castle while the rest of the Cats split up and go round the sides and back of the Mutants' fortress. Cheetara encounters Jackalman, Tygra runs into Monkian and Panthro squares off with Slithe. All three Mutants are easily overpowered by the Cats.
In the meantime, Lion-O manages to locate the Brute-Men's cells and sets them free. Slithe arrives and after witnessing the freed Brute-men, he decides to turn the situation to his advantage. He throws a canister of Warp Gas in the midst of the Brute-men and the vapors cause the meek creatures to turn into raving monsters and they start attacking Lion-O. They then turn their attention to Panthro who has just arrived inside the Castle but just as they are about to attack Panthro, the effects of the Warp Gas wear off and the Brute-men revert to their docile nature. Slithe throws another canister of the gas but Lion-O uses the Sword of Omens' force field to push the gas back towards the Mutants who now end up being on the receiving end of the Brute-men's rage and quickly retreat inside the castle. The Brute-men rejoice at being freed and return to their homes.
- WilyKat notes a Monkian is below them, referring to the character Monkian. This begs the question, where are the other Monkians, and why are they absent in the episode?
- This is the first episode in which the Thunderkittens are told to stay home to guard Cats' Lair.
- Tygra gives two Morals in the episode.
- "Everyone understands freedom, even those who would deprive others of their freedom."
- "Rules are only meaningful if people agree to follow them. Otherwise they're just words."
Slithe: "So, I face the great Panthro. I am not impressed, panther".
Panthro: "You're no work of art yourself, you scaly reptile. Let's see what you've got, Slithe".
Lion-O: "Will the Eye of Thundera penetrate, stone? We'll soon know".
Tygra: "These poor creatures can't help what they're doing, Lion-O. You must fight them".
Lion-O: "I won't fight them! But the Lord of the ThunderCats can't run.
Cheetara: "Lion-O, pride can be a good thing, but pride carried too far is foolishness!"