Third Story Flat Did you ever wonder what it would be like to be murdered in cold blood by your spouse? Well, in Agatha Christie’s "Third Story Flat", and the movie "A Cornish Mystery", This is exactly what happens. In this essay, I will write about this, and many other similarities, and differences of "Third Story Flat", and "a Cornish Mystery. In the "Third Story Flat", the action takes place all in one night. However in "A Cornish Mystery", The action takes place over the coarse several days. Also, in the story, the action took place in the big city, while the movie mainly took place in a small town.