Having watched all of the Star Trek TV series episodes many times each since the 1960s, most being quite good to superb, and only very few being mediocre, my opinion is that this one is the worst of all.<br /><br />In fact, I think it's so poorly executed as to be an embarrassment to the series. It's not that the story is so bad, although it's not particularly outstanding in any way, but the acting is just abysmal on the part of the two lead characters, meaning those other than the regulars in this case. Barbara Anderson gives her weakest performance ever as the daughter of a mass killer, and who is on a mission of a sort. She practically calls in the role from a phone, and shows no real emotive abilities here. Although usually she's never used as more than a pretty face in most of her film/TV roles,usually small parts, she has done much better.<br /><br />Arnold Moss as her father gives new meaning to the term 'Ham' and is the only actor ever on a 1960s Star Trek episode that outdid William Shatner in this area, and actually makes Shatner look superb by comparison. And he gets to play a Shakespearian actor no less, which gives him more impetus to overact, and he does so.<br /><br />Other than these two leads being so weak, the story is such that anybody with any sense at all can tell who the killer is within the first 15 minutes. I say this because I told my brother the whole plot ending at the first commercial break when we were watching the original 1966 broadcast as pre-teens. His reply was, Yeah, you're right.<br /><br />Skip this one and watch the much superior Menagerie episodes which were originally televised right before.