In the novel The Murder of Roger Ackroyd, Mrs Ferrars was a widow who poisoned her husband Ashley Ferrars, a mean drunk man. She is described as a "widow, fairly young still, very well off, good health, and nothing to do but enjoy life". She commits suicide at the start of the novel, in the night between 16 and 17th of September. The reason of her suicide was that, knowing that she had killed her husband, Mrs. Ferrars got blackmailed. Before suiciding, she sent a letter to Roger Ackroyd, who then is found stabbed in his study room. The majority of people in King's Abbot believed that Mrs Ferrars would have married Roger soon.
In the The Murder of Roger Ackroyd episode of the ITV series Agatha Christie's Poirot, Mrs Ferrars was portrayed by Rosalind Bailey. Here she is given the name Dorothy Ferrars and has a parlourmaid too, called Mary. In this episode it is not stated how or why she killed her husband Ashley. In the original version Mrs Ferrars kills herself at the beginning of the story, while in the episode she can be seen considerably later while talking with Roger Ackroyd. In this version Mr Hammond is the Ferrars' lawyer too, aside from Ackroyd's.
The character of Ashley Ferrars, instead, doesn't appear onscreen.