I've heard a few notable writers of Doctor Who day that Episode Three of a four-parter is the most difficult segment to write, as it is often the episode that is the calm before the storm that is Episode Four. The main function of Episode Three is to keep the momentum of the first two episodes going, but not to steal any incident from the final instalment. It usually leaves room for villains to outline their plans for world domination, but also for strong character scenes - the latter of which we get in remarkable fashion in The Ribos Operation.
The scene in question, of course, is the conversation Unstoffe has with his new found friend, Binro the Heretic, who has been cast out of society because of his way out ideas that Ribos was a spherical world that revolved around a sun. The scene is a long one - three minutes - in which no added plot strands are created or wrapped up, and yet it still stand as one of the most beautifully written and performed scenes in Doctor Who history. It comes as no surprise that this scene came from the pen of Robert Holmes, as this scene is also a window in the way that most people on Ribos think and behave. Ribos is just another planet that a Doctor Who story takes place on, but, through the sheer genius of throwaway comments in conversations sprinkled throughout the story, we find out about the planet's seasons, it's culture and traditions, and the rampant superstitious nature of it's inhabitants.
Binro's plight mirrors that of Galileo on Earth in the 1600s and how he was shunned and scorned for the same reasons that Binro was ostracized (and we all know who proved to be correct in the long run). When Unstoffe sits patiently and listens to Binro's wild tale, a tale that he has spun to the ears of a thousand scoffing Ribosians, and then says to the poor man, "Binro was right", it's not only validation of Binro, but of science and reason across the universe. When Binro cried, so did I.