Anne Mulhall is a doctor in astro-biology, but is wearing red instead of a science/medical blue uniform.
Kirk at first opposes Spock beaming down with him. After two seasons of always beaming the three most senior officers into any situation -- known, unknown or actively hostile -- it seems odd that here he's concerned with leaving the ship without its two senior officers.
Why did Dr. Anne Mulhall smile when McCoy said his good metabolic rate is back to normal?
Kirk has encountered creatures of pure energy before, in "Metamorphosis," "Obsession," and "Wolf in the Fold," but for some reason claims here that such a thing is impossible.
Kirk: We faced a crisis in our earlier nuclear age. We found the wisdom not to destroy ourselves.
Sargon: There comes to all races an ultimate crisis which you have yet to face... One day our minds became so powerful we dared think of ourselves as gods.
Scotty: You're going to do what?! Are they all right in the head, Doctor?
McCoy: No comment.
Kirk: Just a simple transference...
McCoy: Quite simple! Happens every day!
Kirk: They used to say, if man could fly, he'd have wings. But he did fly; he discovered he had to. Do you wish that the first Apollo mission hadn't reached the moon, or that we hadn't gone on to Mars and then to the nearest star? That's like saying you wish that you still operated with scalpels and sewed your patients up with catgut, like your great, great, great-grandfather used to do... Dr. McCoy is right in pointing out the enormous danger potential in any contact with life and intelligence as fantastically advanced as this. But I must point out that the possibilities--the potential for knowledge and advancement is equally great. Risk--risk is our business.
Henoch/Spock: I'm surprised the Vulcans never conquered your race.
McCoy: Vulcans worship peace above all, Henoch.
Thalassa/Mulhall: I require only your silence. Only you and I will know that Dr. Mulhall has not returned to her body. Isn't that wroth your captain's life?
McCoy: I will not peddle flesh! I'm a physician!
Thalassa/Mulhall: A physician? In contrast to what we are, you are a prancing, savage medicine man. You dare defy one you should be on your knees worshiping?
Thalassa/Mulhall: Oblivion together does not frighten me, beloved. Promise we'll be together.
Sargon/Kirk: I promise... beloved.
Thalassa/Mulhall: Together, forever.
Sargon/Kirk: Forever... beloved. Forever.
Diana Muldaur later became a series regular on Star Trek: The Next Generation. She played Dr. Pulaski for one season.
The credits for this episode credit John Kingsbridge as the writer for this episode. Gene Roddenberry, however, wrote this episode with John T. Dugan providing the story. John Kingsbridge is a pseudonym for John T. Dugan.
Desilu No: 5149-51.
One of the first episodes produced not by Desilu, but by Paramount Television.