Sultry blonde Barbara Lacey saunters into the Night and Day, a St. Louis bar, where she waits hours to deliver a mysterious envelope to a man that never appears. Helen Tattaglia approaches her neighbors Elvin Suggs and his partners Cobra Glynes and Dimond "Di" Redding of the Grapevine Detective Agency. She hires them to trail her "abusive" husband; she also suspects her in-laws, who live across the street, have arranged for her murder. The shady dealings of the Tattaglia family begin to unravel, while they reveal the secret in the envelope.