Mabelle Sainsbury Seale

In the novel One, Two, Buckle My Shoe, Mabelle Sainsbury Seale was a former actress and had met Alistair and Gerda Blunt in India.

Mabelle acted in the same company as Gerda, and knew that Gerda and Alistair had gotten married without his family's knowedge. She later went on a world tour, where she performed in productions of works by Shakespeare and George Bernard Shaw. She mentioned to Chief Inspector Japp that she had appeared in As You Like It at the Oxford Repertory Theatre.

Mabelle entered into a "rash impulsive marriage", which ended almost immediately, and she then resumed her maiden name. A friend provided her with some capital, which she used to start an elocution school in Calcutta. She also helped to found an amateur dramatic society, and did Mission work.

Six months before the events of the novel, Mabelle travelled from India to England, arriving on the same boat as Mr Amberiotis. Mr Amberiotis helped her with some difficulty over her luggage.

About three months before the events of the novel, Mabelle encountered Alistair Blunt as she was leaving 58 Queen Charlotte Street. She told him that she had been a great friend of his wife's, and asked him for a subscription to Zenana Missions.

Mabelle and Mr Amberiotis met again in London by chance, and Mr Amberiotis invited her to have lunch with him at the Savoy Hotel. Poirot guesses that during this meeting, she told Mr Amberiotis that she had run into Mr Blunt, who was her friend's husband. Poirot further guesses that Mr Amberiotis then found out a secret of Mr Blunt's, and began to blackmail him.

Mabelle was invited to tea at Mrs Albert Chapman's flat at King Leopold Mansions, and was given an overdose of medinal in the tea, which killed her. Her face was beaten to suggest that the body was really that of someone else, so that the police would then look for Mabelle, rather than the murderer.