In the novel One, Two, Buckle My Shoe, Mrs Merton is a resident of King Leopold Mansions in Battersea at unit 82. According to the porter, she was the person most closely acquainted with another resident, Sylvia Chapman at unit 45. Chief Inspector Japp and Poirot approached Mrs Merton for background information on Mrs Chapman after the body of Mabelle Sainsbury Seale was discovered in her flat.
According to Mrs Merton, she only knew Mrs Chapman slightly. They had played bridge a few times, and occasionally went shopping or to the movies together. She also knew that Sylvia's husband Albert Chapman was supposedly a commercial traveller working for some armaments firm and was seldom home. Mrs Merton then revealed that once, when watching a movie about spies, Mrs Chapman had, indiscreetly it seemed, revealed that her husband worked for the Secret Service and that the armaments firm job was only a blind.
Mrs Merton is described as "a loquacious lady, with snapping black eyes, and an elaborate coiffure". She needed no pressure to talk and seemed only too happy to "rise to a dramatic situation".