A series of murders of women on the peaceful planet Argelius II in 2267, for which Montgomery Scott was the suspect until the killer was exposed as the ancient entity Redjac.
Scott was on medical leave on Argelius II, recovering from a head injury, when a dancer named Kara was stabbed in the fog and he was found over the body holding the knife. Two more women died in his presence: Lieutenant Karen Tracy and Sybo, the wife of the planet's prefect, during a ritual meant to find the truth.
The Original Series episode Wolf in the Fold moves the inquiry to the Enterprise, where the computer links the killings to unsolved murders on many worlds, back to Jack the Ripper on Earth. The culprit is a non-corporeal being that feeds on terror and currently inhabits the administrator Hengist.
Driven out, it takes over the ship's computer. Spock occupies the computer by ordering it to compute pi, the crew are tranquillised, and the entity is beamed into space at maximum dispersion.