This is one of the best episodes. It has a haunting, pensive quality, similar to the feeling of some Twilight Zones. I've been thinking of how LIS differs from the original Star Trek of the same era. LIS could be very silly, but so could TOS (1920's gangsters? Ancient Rome planet? Etc.). I think it comes down to this: LIS had kids as main characters, TOS did not; and thus many, or really nearly all episodes of LIS were kind of on the kids' level, while for TOS, it was on a teenager's level--space battles, "fulton torpedoes," women in sexy outfits, etc. That said, many LIS episodes make a strong impression. This is one of those. A fine episode.