- Violet Hunter – A governess and Holmes's client.
- Mr. Rucastle – Hunter's employer, an apparently friendly man with a terrible, terrible temper.
- Mrs. Rucastle – Mr. Rucastle's second wife, fanatically devoted to him and to their young son.
- Miss Alice Rucastle – Mr. Rucastle's daughter by his first wife, subject to an extortion plan engineered by Rucastle.
- Mrs. Toller – A family servant, loyal to Miss Alice Rucastle.
- Mr. Toller – Also a family servant, always drunk.
- Mr. Fowler – Alice Rucastle's fiancé.
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