Synopsis: Successful mystery novelist Janet Frobisher, who has been separated for years from her husband, a man with a criminal past, lives in an isolated home in England. Her nearest neighbor is nosy veterinarian Dr. Henderson. Janet falls in love and occasionally dabbles with her secretary Chris' fiancé Larry, who is years younger than she. When her estranged husband unexpectedly appears, Janet poisons him by administering horse medication given to her by her neighbor. One of the deceased man's criminal cohorts arrives as she's preparing to dispose of the body in the local lake. When Frobisher's secretary and Larry arrive at the secluded house, the mysterious man, who has assisted her with her scheme, impersonates the long-absent spouse of Janet, who plots to get rid of her unplanned accomplice, as well.