During a survey of Alfa 177, a transporter malfunction separates Captain Kirk into two people–apparently, his good and evil halves.

The beginning of two important (ha!) themes in Trek: transporter malfuncitons and evil duplicates. Spock and McCoy wax philosophical about men being made of both good and evil. Yeoman Rand is nearly raped, and her reaction to this was "I wouldn't have said anything . . . I don't want to get you in trouble." And this is simply accepted by the others. Times have changed.