Il caso della domestica perfetta e altre storie

I'm curious whether these stories were written with the idea of being the last for Miss Marple or if they were selected later. Did the author have a specific ending in mind for her?

The stories seem to give a deeper insight into her personality and worldview. I wonder if this was intentional or a result of her being portrayed in her final cases.

The collection feels like a fitting farewell, but I'm curious what drove the decision to compile these stories as her 'final' cases—was it Christie’s idea or the publisher’s?