Lacking a central focus and poorly put together, this "on the run" story is a bit of a muddled mess that is a fan favorite nonetheless for guest star Julie Newmar (more famous as Catwoman on ABC's Batman) and for its Spock, Kirk, McCoy richness.
Using the episode as a personal clearing house of ideas, writer . Fontana tosses in some McCoy backstory, a Klingon, a coup, an unwanted pregnancy, and a wild goose chase. Unlike Babel, where all the elements tie together in an exciting climax, here they tend to meander and become lost amidst random violence.
Unfortunately, the execution of the script does it no favors either. The first half, shot indoors, includes poorly lit and edited scenes that appear grainy, especially on modern televisions. The second half, shot on location at the Vasquez Rocks, has a better look, but curiously has some lighting issues of its own. Taken in totality, the results look like a rushed effort, a common truth that TOS usually disguises better.
Fortunately, Kelley, Nimoy, and Shatner are able to make something out of just about anything and here they give the story some wonderful moments that reward those who hang with it. Fontana's script invests in Kelley in particular, allowing him to carry the A story while Jimmy Doohan carries a B story aboard the ship in a refreshing change of pace from the usual Shatner/Nimoy vehicles. (The episode also sets itself apart with a new, full length musical score by Gerald Fried).
Still, Fontana and company are capable of much better, which is probably why this one, the third of the season to be shot, was originally hidden in the middle of the pack, being the 11th to air. (It actually features the first shot in Star Trek history to include all seven main TOS actors, if you accept George Takei's appearance on a viewscreen. Coincidentally, the last shot featuring the same seven actors together, coming twenty four years later in Star Trek VI, includes the same six actors in person and Takei on another viewscreen. Isn't symmetry a pretty thing?)
Remastered: Keeping it vanilla, the new version doesn't do much more than replace the shots of the Enterprise and the planet (originally a tinted version of Deneva from "Operation: Annihilate!") and keeps it simple at that, with the new Earth-like planet appearing more CGI than CBS Digital's usual efforts. The team does clean up some matte lines on the viewscreen in the opening, adds some detail to a chart Chekov uses for reference, redoes a Klingon ship seen from afar, and redoes some phaser shots at the end... though none of the shots are very fancy.