TOS Season 1 Episode 7 What Are Little Girls Made Of

Plot

The USS Enterprise, under the command of Captain Kirk, travels to the icy planet Exo-III to search for the exobiologist Dr. Roger Korby (played by Michael Strong). Korby was the fiancé of Dr. McCoy's temporary assistant, Nurse Christine Chapel, who signed on to the Enterprise to search for Korby.
At Korby's request, Kirk and Chapel beam down alone to a cavern entrance, but Korby is not there to meet them. Finding this suspicious, Kirk has two security officers beamed down from the Enterprise. One is instructed to stay at the entrance and keep a lookout, and the other accompanies Kirk and Chapel. The three begin to descend into system of caves. When passing over a deep chasm, the security officer disappears. Shortly after, they meet Korby's aide Dr. Brown. Chapel recognizes him but is surprised the man does not remember her. Brown assures them that the security officer fell by accident, and the three continue on. Kirk contacts the remaining security officer and tells him to contact the Enterprise for reinforcements, but a strange creature kills the officer before he gets the chance. Meanwhile, Kirk, Chapel and Brown find Korby, who tells them that the caves were left by an extinct race. Korby shows Kirk and Chapel machinery that creates androids. With the help of Ruk (played by Ted Cassidy), a still-functioning android from the time of the original inhabitants, Korby has created more androids, one being a beautiful woman he calls "Andrea". Brown is also an android. It is also revealed that Ruk had killed the security officers.
Korby creates an android duplicate of Kirk as Chapel looks on. As Kirk's personality is imprinted on the android, the real Kirk imagines himself insulting Spock as a "half-breed". Korby has the duplicate Kirk beamed aboard the Enterprise with orders to identify a planet suitable for creating more androids. When Spock questions the Kirk-android's orders, it repeats the insult Kirk had used. Spock, realizing that this is not Kirk, forms a security team to follow the Kirk-android back down to Exo-III. When it reaches the planet, the Kirk-android encounters Andrea, who destroys him when he refuses to kiss her.
The real Kirk convinces Ruk that Korby is a threat to his existence. Ruk begins to recall the clash between the "Old Ones" and the androids that led to his civilization's demise centuries ago. Korby enters, and Ruk confronts him, but Korby destroys Ruk with a phaser. Shortly afterward, in a struggle with Kirk, the skin of Korby's hand is torn, revealing that he is also an android.
It is now revealed that Korby, dying of frostbite, had transferred his mind to an android body. He begs Chapel to believe that he is still the same man, but Chapel is repelled by what he has done to himself. Andrea, realizing she loves Korby, kisses him, and in despair, Korby fires Andrea's weapon between the embracing pair, destroying them both.
Spock arrives with the security force, but finds that the crisis has passed. When Spock inquires about Dr. Korby's whereabouts, Kirk replies, "Dr. Korby was never here." Chapel decides to stay on with the Enterprise and finish out her tour of duty. Spock tells Kirk about his dismay of using the term "half-breed" to warn that something was wrong. The captain says he will remember this should he find himself in a "similar situation."