In the novel The Sittaford Mystery, Beatrice is the parlourmaid maid of Mr and Mrs Gardner in Exeter.
When Inspector Narracott visited the Gardners as part of the investigations into the murder of Captain Trevelyan he at first did not reveal to Beatrice, who admitted him, that he was a policeman. He pretended to be from the office of the lawyer Frederick Kirkwood. This put Beatrice at her ease and she provided some background information on the Gardner family. She also alibied Mrs Gardner, explaining that during the day of the murder, her mistress had gone out in the afternoon shopping and then went to the cinema. She got in about six o'clock.
However, as Emily Trefusis learnt from Beatrice on her visit to the Gardners, the alibi is not airtight. Beatrice didn't actually see her mistress come home at six. She went to take hot water to Mrs Gardner's room and had a shock when she found Mrs Gardner in bed. Mrs Gardner told Beatrice she had come home at six. Emily consulted the train timetables and found a six ten from Exhampton that got to Exeter at twenty-three minutes to seven, time enough for Mrs Gardner to get home and meet Beatrice at seven in her room.