For the World Is Hollow and I Have Touched the Sky
McCoy's self-diagnosis reveals a terminal disease, but he's well enough to explore a traveling asteroid with inhabitants who believe they're on a planet.
Here we begin the dreaded Season Three journey into mediocrity. It's hard to say this is a bad episode, but what's the point of it? The ship-planet-asteroid-whatever is too confusing to provide much of a sense of wonder, much less build a story around. McCoy's illness comes and goes too quickly for us to feel much sympathy, and there's never a doubt that he won't be fine in the end. The priestess's appeal is a mystery - she has zero chemistry with Kelley. It's a shame this is as close as the doctor comes to a steady relationship, given his warm, compassionate nature. Anyway, the computer has too many silly methods of attacking our heroes: lightning zaps, heat panels, voluntary (!) chips in their brains - painful stuff. And after all that, we push a few buttons et voila? Okay. While they do get Yonada (whose people we never see) back on track, the show soon runs off the rails.
Spock Saves the Day: Spock removes McCoy's chip, gains access to the Book, fixes Yonada's engines, and finds a cure for the good doctor's ailment in the computer banks.
Oops: More inactions to criticize than inactions; why let McCoy stay in this silly place? Well, Spock probably knew he'd be back.
Developments: Since Yonada's systems were "remarkably similar to Federation technology" it isn't too impressive that Spock can work them. His recognizing of Febrini symbols is better, but again this was more to service the marginal plot than Spock's development.