The Agatha Christie Hour: In a Glass Darkly (1982)

In the period prior to World War One Matthew Armitage is a house guest of the Carslake family for a weekend party, and, in the mirror, sees an image of Sylvia, the daughter of the house, being throttled by a man with a scarred neck - just as Sylvia's fiance is similarly scarred. Matthew fights in the war and afterwards returns,scarred mentally and physically, to marry Sylvia. He becomes irrationally jealous of her and realises that he is the man whose face he saw in the mirror. How can he stop himself from murdering his wife?