Gladys Lyndon

In the novel Three Act Tragedy, Gladys Lyndon is Sir Bartholomew Strange's secretary. At the time of the events of the novel, she had been with him for three years.

After the death of Sir Bartholomew, she assists the police in going through his papers, but can provide them no indication as to a likely motive. Poirot and Mr Satterthwaite also interview her, and ask her about a patient of Sir Bartholomew's, Mrs de Rushbridger. Miss Lyndon tells them that Mrs de Rushbridger was only mentioned in Sir Bartholomew's casebook in purely professional terms, and he had never spoken of her in anything other than medical terms.