This Side of Paradise - S1-E25
Plot hole: When Captain Kirk is the last person unaffected by the spores, he's on the bridge lamenting the fact that he is trapped in orbit above the planet since he can't pilot the ship alone. He also can't call for help because Lt. Uhura sabotaged long range communications. but Captain Kirk has somehow forgotten about the shuttle craft. He could have easily escaped on one of those.
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.