Season 14, 4th story, January 1977.
I thought this was going to be one where the Doctor had visited the planet before and created a terrible legacy, like violating the Prime Directive, which interfered with the natural development of the local society, but it turns out that the computer that they worship like a god is only partly the Doctor’s fault. And he references the past trip to the planet but they should have made this a revisit to a planet we’ve seen before. Anyway, it’s a fairly decent plot and this is the introduction of the companion Leela, of which I am a fan. I liked this one.
Next up: The Robots of Death