A seemingly psychopathic killer strangles waitresses on Monday nights and leaves lipstick crosses on their foreheads. Jane Wyman plays a restaurant owner and Nancy Rennick is victim number four. “The Investigators” begin tracking down a mysterious killer who preys on waitresses, but not in time to prevent the death of another young girl employed by restaurant owner Elaine, played by guest star Jane Wyman.

Russ Andrews befriends a shy young waitress, Marla Jensen (Nancy Rennick), at Elaine's, but she fails to fake him into her confidence, refuses protection, and turns up as the killer's next victim

Andrews’ investigation then leads him to Walter Keeler (Peter Leeds), a fast-talking salesman who had been observed bothering Marla in the restaurant the night of her death. Keeler establishes a clear-cut alibi, however, putting a new light on the case.