It's a good thing this episode was not aired back-to-back with the previous one, because this is simply a lower budget version of that much better episode. In fact, this looks to be the episode they needed to get them back on their production schedule and save a little bit of money. Thus, it has no guest stars (have there been any other such episodes before this?), not a single phaser fired, no use of the transporter, no original music, and not even any stars for much of it. The effects shots are mostly stock footage with elements missing, looking much like they might look at some middle point in the process (at one point a blue matte line is very visible). I bet this episode saved a lot of time and money.
And though it didn't turn out completely badly, everything here feels pretty familiar. From the mysterious and deadly creature (about to reproduce, no less), to the power drain, to the bickering between Spock and McCoy, to Kirk leering at a lovely yeoman, everything is bordering on automatic at this point in the second season. Ship-in-danger themes will become the norm in later incarnations of the series, and this episode is a perfect example of why they don't work: the audience knows that the ship will survive, that all the characters will survive, that everyone will be enjoying their shore leave within 48 hours of the end of these events. The peril -- except on the rarest of occasions -- always seems contrived. The solutions always seem like quick fixes -- often built around some deus ex machina "tech" solution ("Maybe if I crossed the flibbernator with the fluorotron generator and fed the stream through the carburrito...").
The peril here is at least reasonably well-conceived (so to speak). It culminates in Kirk's observation that humans could one day be the antibodies fighting a virus much larger than themselves. Not bad. Unfortunately, beyond this scene, not much is done with the concept. Instead, the time is devoted to things more mundane, and generally less interesting: a starship with a Vulcan crew (which falls squarely into the "wouldn't it be cool if..." category), a missed date with shore leave (allowing for much glistening sweat, fainting, many dramatic hypo appearances and medical concerns about stimulants), and multiple rockings of the camera -- er, ship (which catapault at least one poor stuntman over the bridge railing, and Koenig into something approximating a drunken stumble).
The episode doesn't really even get off the ground until it comes time to decide who will go out in the shuttlecraft. Here a character is finally faced with a truly difficult decision, but the tension is cut hopelessly short. From proposition to resolution, this part of the story takes mere minutes. It could have been the focus of the episode, letting go of all the lesser nonsense. A better script would have let Kirk's problem appear gradually and simmer much longer until the only conceivable solution was to send someone out into it. Then let Kirk stew for a bit before making his inevitable decision.
Knowing they had essentially pulp science fiction on their hands, it seems as if the writers slipped a few suggestive concepts past the old censors. How else are we to explain Kirk's pregnant pause (twice) before the word "planet," and some potentially giggle-inducing uses of the word "penetration?" I bet this episode was a lot more fun to make than it looks.
The episode is competent, not sterling. It is cheap, not innovative. It is partially character-driven, but too often distracted. There are worse. There are better.
Rating: Middle (4)