As the first season began to wane, so did the quality of the work. Everyone tired, and some of the intensity of the early days was gone. This episode is certainly based on a good idea (though it does foreshadow "City on the Edge of Forever" a little bit uncomfortably), but the execution is rushed, and some of the internal logic a bit strained. Accepting time travel as a premise is not the problem. Rather, it is the convoluted pseudo-scientific goop required to set up and resolve the crisis which wears very thin. The technical improvisation at the end strains even the most forgiving sci-fi lover.
Add to that the fact that this is a pure problem-solving episode, virtually devoid of character growth in either the regulars or the guest. There is a specific task at hand, it leads to some interesting situations, but we do not come away knowing anything more about anyone, nor is anyone changed by what happens. In fact, the guest is left literally unchanged as he will have no memory of the events which transpired. This is disappointing. A better result would have been to have Christopher remember and realize the importance of what he has seen and learned, and been motivated to keep it to himself. Thus, he is changed, but the timeline is not. The beam-back solution, in addition to being questionable in its logic, is something of a cheat.
The closest we get to growth among the regulars is Spock being outed as fallible. Unfortunately, the audience has not been led to understand the character the way the writer has. Because of his memorable emotional outbursts already, the audience does not regard him as a coldly perfect machine, but as a tortured soul trapped between logic (rigorously coherent reasoning, not mechanical precision) and emotionalism. Thus, McCoy's taunts on this matter always seem to miss the mark. They are forgiveable primarily because their sole purpose is to reinforce the basis for the relationships, a necessary thing in episodic television.
Of course, it also adds levity. But levity is also a bit of a problem here. Virtually everything seems to be played for belly laughs while only being, at most, gently amusing. Spock is portrayed to the guests as the proverbial "little green man" of legend. Maybe it's a funny characterization, but it's just plain overdone by adding funny faces and comic musical cues. When Trek humor bubbles up from the characters (rather than the situations) it always hits its mark. The reverse is seldom true. (This goes for non-Trek writing as well, of course.)
There is even another lame attempt to give Barrett something more substantial to do. It's as if she simply got tired of doing the regular computer voice and convinced someone to write her something more interesting. It sticks out like a sore thumb.
But part of the problem is that the characterizations have begun to grow mannered all around. The script is partly to blame for serving up a series of character cliches which, even when amusing, reduce the depth of the characters which has been built up through the first 20 episodes. Thus, Shatner's Kirk has become smarmy and adopts an all-knowing grin which is very unbecoming of a starship captain. Spock has settled into seriously stone-faced. And McCoy is virtually irrational as he bleats at Spock. Director O'Herlihy plays up the comic elements, perhaps knowing that the story strains credulity a bit.
Motivations are also somewhat random. Guest star Christoper (played variously steely and jovially by Roger Perry) vascillates between content, curious and cooperative, and cunningly escape-happy. Kirk appears to not even consider any consequences before inviting Christopher to the bridge, giving him a uniform, and assigning him guest quarters (with presumed free run of the ship). While these serve the plot, they run directly counter to what we have been taught to expect of the characters.
In technical areas, Westheimer is put to the test with a large number of optical effect shots. The results are decidedly mixed.
Some of the effects are positively stunning. Unlike the parallel Earth in "Miri," shots of the Earth from space now have a wispy atmosphere (except when viewed from the bridge's main viewscreen, which is obviously a reuse of the earlier effects by Cinema Research). And the image of the Enterprise floating in a blue sky is quite arresting (despite the fact that it moves somewhat erratically). But the opticals take a nosedive later when the ship is buffeted about and the model's support structure flickers noticeably into view several times. The ship's movement during the climactic return to its own time looks like it was rushed through production.
Despite its sometimes heavy tone, this episode appears to have been an attempt to keep things light while digging into serious sci-fi territory. But it does this at the expense of the characters and Trek's generally more coherent concepts. By this point, Fontana had already done many uncredited great things for the series. This one is a misfire. She can, and would, do much better.
Rating: Middle-Lower (5)