Plot

Nurse Chapel is reunited with her fiancé; but his new obsession leads him to make an android duplicate of Captain Kirk.

The crew of the Enterprise arrive at the planet EXO-III with some trepidation and great anticipation. They are there to see if hey can locate the renowned scientist Dr. Roger Korby. The man hasn't been heard of for 5 years and the general belief is that he is dead. For Nurse Christine Chapel however, a reunion with Corby will be a reunion with her fiancé. They find Korby alive but when Kirk and Chapel beam down to the planet, they find a man obsessed who is using alien technology to reproduce the humans around him in the form of androids.—garykmcd

Kirk and Christine Chapel beam down to Exo III, looking to find her missing fiancé, Roger Korby. They find him being protected by the ancient android Ruk and assisted by the beautiful Andrea. Korby has become obsessed with the possibilities of Android replacements and produces an android duplicate of Kirk to prove his point.—The TV Archaeologist

In search of Nurse Chapel's fiance, renowned exobiologist Roger Korby (Michael Strong), the Enterprise visits the icy planet Exo III. His last message was 5 yrs ago where he talked about finding underground caverns. Since then 2 expeditions have failed to find Korby. But Korby responds to the Enterprise. Kirk beams down with Chapel and 2 security men. One of the men is pushed down a bottomless pit by an unknown assailant & the 2nd one is murdered, when Kirk is distracted by Dr Brown (Harry Basch), Korby's assistant.

Kirk meets Korby, who stops Kirk from establishing contact with the Enterprise. Brown draws phasers on him, but Kirk shoots him, revealing that Brown was an android. Kirk is controlled by the unknown assailant, whose name is Ruk (Ted Cassidy). RUk was found on the planet by Korby, protecting the machines left by the old ones. Korby has discovered an ancient machine which allows him to duplicate any living person with an android replacement. And a young girl android, Andrea (Sherry Jackson), who is dressed in an unusual jumpsuit resembling red suspender bottoms with straps, with no blouse. She is also an android created by Korby.

Kory demonstrates the results of his experiments to Kirk & Chapel. Korby plans to use the machine to spread controlled androids throughout the Federation. Eventually Korby says by continuing his work he can transfer entire consciousness into an android. Korby wants control of the Enterprise to travel to a planet with the proper raw materials to continue his experiments. Korby brings Christine into an experiment chamber. He says "Here is how you make an android. He pushes a switch, and the table swivels, revealing Kirk. On the other side is a putty form. He spins the controls and the machine turns wildly. As it is spinning, Kirk says over and over quietly "Mind your own business, Mr. Spock. I'm sick of your half-breed interference." He wants the phrase inside the android Kirk's mind.

As Kirk expected, Korby sends the android up to the ship to give orders to Kirk's crew, in order to to help Korby take over. Spock stops the android in the hallway and says "Captain, are you alright?" And the android Kirk snaps at him with the prejudiced phrase "Mind your own business Mr. Spock. I'm sick of your half-breed interference!". Spock knows something is wrong. Down on the planet, the real Kirk stirs up Ruk's anger (Kirk reminds RUk that the old ones created him and the androids killed the old ones as they were not logical. The Androids are making the same mistake with Korby and Kirk makes Ruk realize that one day Korby would have to be killed too). As Korby enters the room, Ruk moves toward him to kill him. Korby disintegrates Ruk.

Next Kirk finds Andrea. He says "Andrea, kiss me." Again, she kisses him softly. Then she is about to slap him, and he grabs her and kisses her some more. She is weak and dizzy. The android has beamed back down and is preparing things to bring to the Enterprise. Andrea sees him. She looks at him and says gently "Please kiss me." He says "It is illogical." So she shoots him with a phaser. Korby is in the room holding a phaser on Kirk, but his hand is caught in the door. The skin comes away, and underneath there is circuitry. Korby is an android too. What the hell?? Andrea comes in to report shooting the prisoner and sees Kirk, and recognizes her mistake. Then she moves slowly toward Korby. She says...

"To..to love you. To.. to kiss you." She moves her lips toward Korby's, but the phaser goes off and they are both disintegrated. The ship is saved. Nurse Chapel decides to stay on the Enterprise.