Тайна замка Чимниз

The setting feels so vivid and atmospheric. I'm curious whether Christie based it on a real place or if it was imagined from scratch.

The middle section seemed to focus heavily on character interactions and politics. Was this intentional to build suspense or just a writing style?

His personality adds a lot of flavor to the plot, but I'm wondering if his role was always meant to be so pivotal or developed later.