Mrs Margaret de Rushbridger

In the novel Three Act Tragedy, Mrs Margaret de Rushbridger was a patient at Strange’s sanatorium. She arrived there on the day Dr Strange was murdered. She is about forty years old, and has dark hair.

According to the Matron at the sanatorium, Mrs de Rushbridger had suffered a bad nervous breakdown, with lapses of memory and severe nervous exhaustion. She was put on a very strict rest cure, and was not allowed any letters or exciting visitors. She had recently arrived from the West Indies, and her husband was still out there.

Poirot later receives a telegram from Mrs de Rushbridger, saying that she can give important information regarding Strange's death. However, when Poirot and Mr Satterthwaite arrive at the sanatorium to see her, they are told that she is dead. A box of liqueur chocolates had arrived for her by post, and she had eaten one, and died a few minutes after. The chocolates in the top layer of the box had been tampered with, and the poison was thought to be nicotine.

It is later revealed that the telegram from Mrs de Rushbridger was actually sent by the murderer. The murderer was using her to divert suspicion from themself, but had to kill her to prevent her from telling anyone that she actually knew nothing about Strange's death.

Portrayals
In Murder in Three Acts (1986), that name of the character is simplified to "Mrs Rushbridger". Although she appears in one scene, she is portrayed as catatonic. She was later murdered by means of chocolates which had been spiked with "Benzotine". The actress who played her is not credited.

In the film adaptation of Three Act Tragedy in Series 12 of ITV's Agatha Christie's Poirot drama series, Mrs de Rushbridger does appear but the actress who played her is not credited.