The one where the Gonds are finally liberated from the Krotons...
In episode 3, Eelek claims that the Gond Council has taken a vote in Selris's absence and elected him as leader, thus ousting ol' scrunchy-face. But here, Selris claims that leadership of the Council is hereditary, and so his son Thara will be next leader. If this is the case, then how and why did the Council hold a leadership election at all? If they were looking for a new, young, fresh, robust, strong and stable leader, why not just turn to Thara, who has been just as outspoken about the Krotons - if not more so - than Eelek? A bit of muddy world-building from Robert Holmes there, I fear.
For the first time in the story, the Gonds get to lay eyes on their Kroton masters when one of them comes out of the Dynatrope to demand that the High-Brains (the Doctor and Zoe) are bought to them. Why they didn't just use the booming voice we witnessed in episode 1, I'm not sure, but the emergence of this crystalline creature certainly strikes awe into the people. Seeing the Kroton shuffle down the gangway, its skirt swishing, struck me as terribly silly. They really are terrible in long-shot!