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E2 Star Trek episode guide : Original Series : Season One

The Enemy Within

Episode number:
Airdate: October 6, 1966
Stardate: 1672.1

Writer: Richard Matheson
Director: Leo Penn

Regulars: Kirk, Spock, McCoy, Scotty, Sulu, Yeoman Rand
Others: Lieutenant John Farrell...Jim Goodwin
Technician Fisher...Edward Madden
Technician Wilson...Garland Thompson


I have the feeling that this episode perhaps more than any of the other early episodes embodied what Gene Roddenberry had in mind for the series: a top flight science fiction author, Richard Matheson, tackling issues of philosophical weight. The issue here is the nature of good and evil, provided by an interesting twist on the Jekyll/Hyde theme. The good Kirk and the evil Kirk need one another to survive. The good Kirk is compassionate and intelligent, but indecisive and weak, and needs the strength of the violent, evil Kirk to be an able Captain.

Story (with spoilers)

During a scientific expedition on Alpha 177, Geological Technician Fisher takes a minor spill and ends up covered in some yellow magnetic ore. Kirk orders him to beam up to sick bay for treatment of his wounds and follows shortly thereafter, leaving Sulu in charge of the expedition. When Kirk beams up, he is a bit woozy, so Scotty helps him out of the room, leaving the transporter unattended. An instant later, a duplicate Captain Kirk appears on the transporter pad. Apparently the magnetic ore has had a strange affect upon the workings of the transporter.

While the first Kirk, the “good Kirk”, is in his quarters, the “evil Kirk” accosts Dr. McCoy and demands Saurian brandy. Then he heads to Yeoman Janice Rand’s quarters for more accosting. Spock drops by to visit the good Kirk asking about the incident in sick bay, but Kirk dismisses it as a prank by the good doctor. Then they visit Scotty in the transporter room. He has just beamed up an animal (a “space spaniel”, as one book describes it) gathered by the survey team and discovered the transporter’s malfunction when a violent duplicate of the spaniel appears. This means, of course, that Sulu and company are stranded on Alpha 177 until they discover the source of the problem.

Meanwhile, Rand fends off an attack from the evil Kirk with the help of Technician Fisher, who is helpfully passing by in the corridor and has saved Desilu the cost of hiring another actor. Fisher gets some more wounds, these from Kirk’s fists meeting his face. Spock and the good Kirk try to figure out what’s going on while a bloody evil Kirk roams the corridors menacingly.

The problem, once identified, becomes more complicated. The landing party is in jeopardy from impending nightfall, which will drop surface temperatures to a lethal level. The good Kirk becomes indecisive and has difficulty making decisions. The evil Kirk, knowing that he can be identified by the scratches on his face made by Yeoman Rand, covers them up with makeup and steals a phaser from Technician Wilson. The good Kirk and Spock hunt the evil Kirk down in engineering and capture him. Unfortunately, he does some nasty damage to the transporter systems before he can be subdued.

While Sulu and company are heating up rocks with their phasers for warmth, and you are wondering why they don’t just use a shuttlecraft to rescue them, the evil Kirk is dying in sick bay. All concerned realize that Kirk needs his “evil” side to remain the able commander that he is because it gives him his decisiveness and his strength. Thankfully, Spock and Scotty have found a way to fix the transporter (the same transporter that Scotty said needed a week to fix a couple of scenes ago) and fix Kirk to boot. It is tested on the spaniel and the animal is put back together successfully, but the shock was too much for it. “He’s dead Jim!”

The indecisive good Kirk wrestles with the risks of chancing the transporter, but can’t make a decision. After chatting with Sulu, who is enjoying the cool -117 degree temperature, he makes his choice. But the evil Kirk will have none of it: he beats up the good Kirk and scratches him for good measure, then heads off to the bridge and orders the ship to break orbit. But McCoy and the good Kirk are hot on his heels for the big good twin/evil twin showdown. As the crew wonders who is who, the good Kirk convinces the evil Kirk to rejoin him before they both die. The transporter puts them back together again and the survey party is quickly beamed up and treated for frostbite.


  • This episode marks the first appearances of Spock’s Vulcan nerve pinch and McCoy’s immortal line, “He’s dead, Jim!”.

  • Kirk’s uniform insignia is missing in several shots, one of many continuity efforts which are perhaps inevitable in an episode with one actor playing two roles.

  • Somebody needs to tell me why they didn’t use the shuttlecraft.