Audiences often find themselves confused with time-travel stories, even when they are done well.
This episode handles the subject so poorly that there's no way even the most astute viewer could reconcile its content.
The Enterprise is accidentally sling-shot back through time due to some sort of encounter with a "black star", which we never see. They encounter a 1960s jet pilot who causes a tough situation for the crew: beam him back to the planet, and risk altering history with knowledge of the future, or keep him and risk changing it due to his absence. It's a paper-thin dilemma that offers no character insight, world building, or considerable dramatic payoff.
I almost wonder of the episode was reverse engineered to allow Kirk to get into hand-to-hand combat with military personnel. The fight itself is fairly well done, but the context is so lacking that you feel guilty for enjoying it.
I'd like to try to explain the ending, but I can't. Somehow, they are able to beam the pilot back into the place he was initially abducted. It's so poorly done in both setup and execution, that I can't tell you if the pilot is supposed to remember the Enterprise, or has his memory inexplicably wiped. It really is an amazingly terrible resolution. It's giving no consequence to the ongoing development of our characters, and no immediate intrigue to at least satisfy your dramatic apatite.
Let us hope that the handling of accidental-time-travel-by-way-of-spacial-anomaly is superior when used in the new film, which is now only a few weeks away. Apologies for my lack of adherence to the initial schedule, whereby all three seasons would have been analyzed by the time of the film's release.