What is the author's style in Curtain by Agatha Christie?

The language of this novel is relatively simple and easy to read. The author, however, interjects many French words to fit into the setting of the novel because Hercule Poirot is French. The language is from the 19th or 20th century, which is when the novel is set, and also seems to have British spellings of some words. The language is descriptive enough that it helps to explain the situations and is always detailed enough for the reader to truly understand what is happening.