Stardate: 1672.1 -16.72.9 - 16.73.5

Original airdate: 10/6/1966

Writer: Richard Matheson

Director: Leo Penn

Guest stars:

Jim Goodwin             John Farrel (navagator)

Edward Madden           Geological Technician Fisher (crewman who fell into a soft yellow ore with unusual magnetic properties which caused the transporter to malfunction causing the 'split' into two opposite halves of a native animal and Capt. Kirk

Garland Thompson        Technician Wilson (transporter tech attacked by the evil Kirk)
 

   "James" (unshown person on the bridge)

Crewmen appearances:
Kirk, Spock, McCoy
Sulu
Uhura (voice only)
Scotty
Yeoman Rand (who was nearly raped by the evil Kirk in her cabin)

Story:

A transporter malfunction splits Kirk into two beings: one pure evil and the other good. What follows is a battle between the two as each battle for supremacy at the expense of the other, though it becomes obvious that they need each other. Spock and Chief Engineer Scott attempt to devise a method of combining the two Kirks into one. Meanwhile, a landing team is trapped on the surface of Alpha 177 and sub-zero temperatures. The Enterprise cannot beam them aboard for fear that what happened to Kirk would happen to them as well.

Alpha 177- planet where the enterprise is doing a study. oxygen atmosphere (they arent in space suits) which goes to 123 deg below zero at night.

Unnamed native animal: dog like with a single central horn and anntenae like projections on head. Specimen was split into to opposite halves by the transporter malfunction caused by Tech. Fisher.

Tidbits:

Phasers: setting #1 (is this the same as stun?)

Spock usues the Vulcan neck pinch to stop the evil Kirk

Study in the human mind:
 negative side: hostility, lust, violence,strong leadership, the will   to live, fear
 positive side: compassion, love, tenderness, courage, but without the   evil side losses the powers of decision and command

Sulu requests hot coffe and rice wine to be sent to the freezing men on the planet

Saurian Brandy: Kirk demands it. It is kept in 'sick bay'

Quotes:

After Kirk and Spock try to decide what to do, Spock keeps pointing out the problems with what Kirk tries to decide, so he says," What I dont know is why I forgot that just now."
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Being split into two halves is no theory with me, Doctor. I have a human half as well as an alien half, submerged, constantly at war with each other. Personal experience, Doctor. I survive because my intelligence wins out over both. Makes them live together."
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The imposter had some interesting qualities, wouldn't you say, Yeoman?

TV guides brief description of the episode:

THE ENEMY WITHIN
No guest stars, so Kirk gets frustated and beats himself up.