Myrtle Dene

In the short story The Thumb Mark of St. Peter, Myrtle Dene is the house where Mabel Denman, a niece of Miss Marple's, lived with her husband and father-in-law. Miss Marple does not state where the house is but describes it as a large house with an extensive staff comprising a cook, maid and a live in nurse who looked after Mabel's invalid father-in-law. From the context, the house is not in St. Mary Mead as Mabel has to write to Miss Marple.