Scotty is accused of murdering women, and an ancient entity is feeding on fear.
Scotty is on shore leave on Argelius II when a woman is murdered and he is found holding the knife. He cannot remember what happened, and investigations suggest he has a hidden hatred of women. Kirk and Spock use the ship's computer and a truth-seeking device to find the real culprit.
The killer is an entity that feeds on fear and has been linked to Jack the Ripper. It is a murder mystery with horror elements and a showcase for the character of Scotty. Fans remember its twist and the sinister, drifting menace of the villain.