“Mirror, Mirror” stands out as the best Star Trek: The Original Series season 2 episode because it fuses a high-concept sci-fi premise with sharp political commentary, unforgettable character work, and a legacy that reshaped the entire franchise. While “The Trouble with Tribbles” and “The Doomsday Machine” are often cited as fan favorites, “Mirror, Mirror” arguably captures the full range of what TOS does best in a single, tight hour of television.
Now, here are five reasons "Mirror, Mirror" is the best episode from the second season of The Original Series.
1. The definitive Mirror Universe story
“Mirror, Mirror” introduced the very concept of a Mirror Universe to Star Trek, using a transporter accident to throw Kirk, McCoy, Scotty, and Uhura into a brutal parallel reality ruled by the Terran Empire. The idea of evil (and often exaggeratedly “sexy”) doppelgangers became so iconic that “evil alternate self with a goatee” is now a pop‑culture shorthand that traces directly back to this episode.
The power of the episode lies in the fact that the Mirror Universe is not just a gimmick, but a funhouse reflection of the Federation’s ideals, forcing the crew to navigate an Enterprise where advancement is earned through assassination and fear, rather than cooperation and trust. Later series from Deep Space Nine to Enterprise would build entire arcs on this foundation, but the original remains the leanest and most potent version of the concept.