Despite his plea of not guilty, a businessman is arrested after a night out, drinking with a woman in a sexy black evening gown in a nightclub. He is accused of strangling his wife to death with his tie, and circumstantial evidences point to him having done it. He is able to bring some witnesses to court, to prove he had been away from home all the evening when the crime was committed. But the witnesses declare they do not remember having seen him - and then they start dying one by one, as the widow waits his death in prison. His last witness is "the woman in black" with whom he had spent the night - and eventually she may be his saving angel.