.

[Linked Image from treknews.net]


STAR TREK original series, season 1, episode 28
"City On the Edge of Forever" ( 50 minutes, link to the full episode, without commercials, first aired April 6, 1967)

https://ok.ru/video/7604846004967


If not the single best episode of the series, and Joan Collins' best performance, certainly up there near the top.
Winner of the Screen Writers' Guild award for best television screenplay of 1967.
And also won a Hugo Award in 1968 for best dramatic presentation.

https://en.wikipedia.org/wiki/The_City_on_the_Edge_of_Forever



And here's the comic book adaptation of Harlan Ellison's original screenplay in comics form, that I linked earlier in a STAR TREK topic. So you can see Ellison's original vision, as compared to the final televised version :
https://readallcomics.com/star-trek-harlan-ellisons-city-on-the-edge-of-forever-001-2014/ ( 5 issue adaptation, probably also available in collected form.)