hears this announcement and uses makeup to mask his injury. He secures a phaser from a security officer, before going into hiding in engineering. Putting himself in his shoes, the "good" Kirk anticipates this move. While the two Kirks scuffle, Spock disables the "evil" Kirk with a Vulcan nerve pinch. Spock and McCoy realize that both Kirks are mentally deteriorating, and they must find a way to reverse the transporter accident to save them, as well as the landing party. Spock and Scott use power from the ship's impulse drive to reverse the transporter on the dog-like specimen. When it materializes, the creature is whole but dead. Spock suggests that it died because its animal brain could not handle the stress of its two halves being reintegrated, so Kirk will be able to survive the same procedure, while Dr. Leonard McCoy insists they can't take the risk that the death was caused by ongoing transporter malfunction. With the landing party nearly dead from hypothermia, the "good" Kirk opts to gamble on the procedure rather than wait for an autopsy on the creature. When he releases the "evil" Kirk, his other self overpowers him, and gives him facial scratches like his own. Pretending to be the "good" Kirk, he tells Rand the truth about the "imposter", and makes a date with her before heading to the bridge. He orders the crew to leave orbit, telling the navigator that the landing party cannot be saved. The "good" Kirk and McCoy race to the bridge, where the two Kirks face off. The "good" Kirk at last persuades the "evil" Kirk that they need each other to survive, and will both live on as parts of each other. He orders Scott to attempt the reversal process, and Kirk is rejoined as one being. With his sense of command and good will restored (and the transporter repaired), Kirk orders the landing party beamed up. They are safe despite the cold. Rand tells Kirk about her last encounter with "evil" Kirk, but he cuts her off before she can discuss the issue of his romantic overtures. Production The episode's writer, Richard Matheson, was inspired by Dr Jekyll and Mr Hyde, Robert Louis Stevenson's character who is struggling with his evil alter ego. The subplot of four crewmembers stranded on the planet in freezing temperatures was added later as a re-write. Matheson opposed the idea as he