Stardate 1672.1: The landing party is conducting a geological survey of planet Alpha 177 when Geology technician Fisher falls from an embankment and is beamed aboard the Enterprise to be treated for an injured hand. After a rough beam-in, Scotty notices magnetic ore covering Fisher when the technician materializes and tells him to have the uniform decontaminated. Kirk beams up next and is unknowingly split into two seperate entities, one kind but weak and indecisive, the other vicious and cruel. Before anyone can determine what has happened, the evil Kirk demands brandy from McCoy and later attacks Yeoman Rand. When an animal is beamed aboard in an identical fashion, Spock makes the connection and concludes that the same thing must have happened to Kirk during a transporter malfunction. With the transporter out, the remaining crewmembers on the planet are forced to wait for repairs, but the nights on Alpha 177 are unbearably cold with the temperature dropping to -70 degrees. Meanwhile, Spock and a weakened Kirk conduct a search of the engineering deck where they find the evil Kirk hiding. They manage to capture the evil Kirk and restrain him in sickbay where Spock formulates his theory that it is the evil half of Kirk where the strength of command resides and that without his negative side Kirk is losing his ability to make command decisions. Worse still, the split appears to be killing the evil Kirk, and neither side can survive without the other. Scotty makes uncertain repairs to the transporter, and the split animal is sent through to be rejoined only to die in the attempt. With time running out, Kirk is convinced by Spock that the animal died from the fright of being rejoined and not due to a transporter malfunction and goes throught the transporter with this evil side. He returnes alive and whole and immediately orders the landing party beamed up, frostbitten but okay.