Mrs. Ferrars

Mrs Ferrars is a wealthy widow in The Murder of Roger Ackroyd whose death opens the novel: Dr Sheppard is called to certify that she has killed herself a year after the death of her abusive husband. She had been engaged to Roger Ackroyd and had admitted to him that she poisoned her husband and was being blackmailed; the letter she posted before her death leads to Ackroyd's murder, and Poirot finds that Dr Sheppard was her blackmailer.