This is one of the better episodes of season three, I think. On the negative side, there's the weirdness of how Kirk manages to fall so deeply in love with an android woman in just a couple of hours, and the fact that he accidentally uses his power to talk computers into committing suicide on her.

But on the positive side, it's a solid exploration of why it sucks to be immortal, which is always a good hook to hang a story on. We get to see Spock play a piano, and be generally taken with the artistic side of life, while McCoy is concerned with the logic and science of getting his fever cure made on time. And there's that intriguing last scene, where Spock takes it upon himself to help ease Kirk's painful memories, which is a very interesting precursor to something that happens later on...

Transcript

1
Captain's log, Stardate 5843.7. Rigellian fever has broken out on the Enterprise. We need ryetalyn to cure it.
Spock: This is a serious infectious disease. Why don't we have any medicine for it on board?
McCoy: PLAGUE!
2
Kirk: This uninhabited planet has all the ryetalyn we need.
Spock: And inhabitants, apparently.
Flint: Get off my planet!
3
McCoy: We need ryetalyn! Have you seen Rigellian fever? It's like black PLAGUE!
Flint: Constantinople, 1334. It stalked the streets, killing. The plague, PLAGUE!
McCoy: PLAGUE!!
4
Flint: I am Flint. Enjoy my castle. My robot will make your medicine. This is Rayna, my ward.
Kirk: {love heart eyes}
{Spock looking at paintings in background}
5
{Kirk and Rayna dance, Spock plays piano}
6
Spock: This music is definitely by Brahms, but unknown. And these paintings, original works by the hand of Leonardo da Vinci.
McCoy: Jim, Flint is human, but thousands of years old!
Caption: Two and two makes... wait for it...
7
Kirk: I don't care about that. I love you, Rayna! Come away with me!
Spock: You love her? We have been here less than two hours.
McCoy: And... the PLAGUE!
{Flint jealous in background (dagger eyes)}
8
McCoy: Flint hid our medicine in here...
Kirk: A secret room!
Spock: Full of prototypes of Rayna. She is an android.
9
Flint: I am immortal! I am Brahms, da Vinci, Solomon, Alexander, dozens of others. But lonely. I made Rayna as my companion, but she had no emotions, until you wakened love in her, Kirk.
Kirk: Time for a fist fight!
Caption: ... Four!
10
Rayna: Kirk has shown me what love is, but now I love Flint too! I am conflicted.
SFX: zzzt! zzzt!
McCoy: Her logic couldn't handle it! You talked her to death, Jim!
Kirk: {Kirk standing over Flint} Dang.
11
{Kirk's quarters on the Enterprise}
McCoy: The PLAGUE is under control.
Kirk: All's well that... no... how can I forget her? I need to forget her, but I can't...
Kirk: zzz...
McCoy: Let him sleep, Spock.
12
Kirk: zzz...
Spock: {mind melding} Forget...