A transporter malfunction splits Captain Kirk into two halves: one meek and indecisive, the other violent and ill tempered. The remaining crew members stranded on the planet cannot be beamed up to the ship until a problem is fixed.
The Enterprise picks up untrustworthy entrepreneur Harry Mudd accompanied by three beautiful women who immediately put a spell on all the male crew members.
Kirk and psychiatrist Helen Noel are trapped on a maximum security penal colony that experiments with mind control and Spock must use the Vulcan mind-meld to find a way to save them.
While Captain Kirk investigates whether an actor is actually a presumed dead mass murderer, a mysterious assailant is killing the people who could identify the fugitive.
The past months have left the crew exhausted and in desperate need of a break, but does this explain McCoy's encounter with a human-sized white rabbit or Kirk crossing paths with the prankster who plagued his days at Starfleet Academy?