If I'm not mistaken, this is probably the very first episode of Star Trek
that didn't have any sort of science-fiction angle whatsoever. (Originally, what became the later episode Remember Me
was going to be a subplot here, but it was ultimately decided to leave it out.) In a way, it also was a major step forward in making Trek
episodes less "stand-alone" and in establishing the viability of greater continuity and story arcs.