#43: The Alternative Factor.
In case you forgot: A madman named Lazarus is determined to be at the center of some weird magnetic nonsense going down. The Enterprise beams him aboard and he tells them that he is in hot pursuit of another person, a creature capable of destroying all life as we know it. Turns out Lazarus is after a parallel version of himself, only the parallel version of himself (Anti-Lazarus, I guess?) isn't really out to destroy anything. He volunteers to stay locked in combat with Lazarus in some safety corridor for all eternity, because if either one of them gets out both universes will be destroyed.
This episode seems to be nearly universally panned by fans, but despite all that I really, properly, almost like it. Hear me out.
The pacing on this episode is different from your standard TOS fare. Usually TOS lays out the problem in its entirety pretty early on and we watch our heroes try to figure out the solution. In "The Alternative Factor" it's clear that for the most part, no one really has any clear idea of what's going on, just some hazy hypotheses about matter and antimatter and a very clearly crazy man running around the Enterprise.
The pathos and drama is played just right, in my opinion; the episode doesn't really sink into melodrama. Lazarus is obviously a seriously unhinged individual and to be trapped with him for the rest of your life is a grim prospect. Whatever the rest of the episode, that part of it is handled with a deft touch.
If you called out Star Trek, especially TOS, on every instance of dodgy science, you wouldn't have much time to actually enjoy the show. I know that, and I'm not doing that here. All I ask out of the series, or at least a given episode, is consistency. For example, Spock asserts that if matter and antimatter meet, that means total annihilation. But that reaction is what fuels the Enterprise. There's not even a wink or a nod to this.
You can forgive such an obvious oversight, of course, by saying, "That part of the canon hadn't been developed yet." That's fair. But that still doesn't explain the fact that antimatter and matter interact (that being Anti-Lazarus and Lazarus) for multiple, protracted periods of time in this episode. If their meeting constitutes the end of the entire freaking universe, then how in the world are the writers defining "meeting"?
Should have been a much better episode than it ended up being. Sigh.