"This is the face of terror: Anne Marie Henderson, eighteen years of age, her young existence suddenly marred by a savage and wholly unanticipated pursuit by a strange, nightmarish figure of a woman in black, who has appeared as if from nowhere and now at driving gallop chases the terrified girl across the countryside, as if she means to ride her down and kill her - and then suddenly and inexplicably stops, to watch in malignant silence as her prey takes flight. Miss Henderson has no idea whatever as to the motive for this pursuit; worse, not the vaguest notion regarding the identity of her pursuer. Soon enough, she will be given the solution to this twofold mystery, but in a manner far beyond her present capacity to understand, a manner enigmatically bizarre in terms of time and space - which is to say, an answer from the Twilight Zone."
A young heiress, Anne, is engaged to be married to a respectable investment broker, while rebellious David Mitchell is trying to get her to elope with him. One day while horseback riding, she sees a terrifying woman dressed in black on horseback, who begins yelling at her to stop. The woman in black gallops toward her at full speed, and the young woman flees in terror, escaping her pursuer. Just before she is to be wed, Mitchell forces himself into her home past the butler, and exposes Anne's father's weakness in the face of Mitchell's overbearing, relentless presence. Mitchell convinces Anne to elope with him.
Twenty-five years later, Mitchell is a dissolute failure, who has driven the ranch Anne's late father left her into bankruptcy, and himself and Anne to alcoholism. Anne has a fight with her husband and goes horseback riding, where she sees herself as a young woman on a horse. She now realizes that she was the terrifying woman in black who had frantically chased her younger self, not to threaten but to warn her not to make the mistake of eloping with Mitchell. Unfortunately, the older Anne is unintelligible to the younger Anne. Anne is her own "ghostly double", who, whenever horseback riding, can see her younger self. However, try as she might she can never catch up, and thus can never change her past/future.
"This is the face of terror: Anne Marie Mitchell, forty-three years of age, her desolate existence once more afflicted by the hope of altering her past mistake - a hope which is, unfortunately, doomed to disappointment. For warnings from the future to the past must be taken in the past; today may change tomorrow but once today is gone, tomorrow can only look back in sorrow that the warning was ignored. Said warning as of now stamped 'not accepted' and stored away in the dead file in the recording office of the Twilight Zone."