In the novel Dumb Witness, Miss Caroline Peabody is a longtime friend of Emily Arundell, and has known her for more than fifty years. She ran into Emily at the greengrocers, sometime before Easter. She knew all the Arundell siblings and shared her knowledge with Poirot.
Miss Peabody knows about some matters concerning the Arundell family, including "certain regrettable lapses" in the life of General Arundell, and certain troubles connected with the younger generation. However, she never spoke of these things with Miss Arundell, as both of them were "upholders of family dignity, family solidarity, and complete reticence on family matters".
When Poirot and Hastings call on Miss Peabody, she immediately asks whether they are selling anything. After hearing that Poirot wants to hear about General Arundell for a book he is writing, she expresses the opinion Hastings, being educated at Eton, could not write decent English.
Miss Peabody tells Poirot that there is something "fishy" about Miss Arundell's will, leaing everything to Wilhelmina Lawson. However, she does not have any exact ideas about it.
Miss Peabody later reveals that she knew who Poirot was, and that he was not writing a book about General Arundell, but was really seeking information on the Arundell family. However, she did not mind talking, as she enjoys talking, and finds it hard to get anyone to listen to her.