What is the author's style in Cards on the Table by Agatha Christie?

Cards on the Table, written in 1936, uses certain language that is sometimes unusual today. From time to time she uses terminology that is considered very politically incorrect in today's society. For example, Christie refers to Shaitana as a "Dago", a xenophobic term for someone who is foreign. The reader must remember that the world is between two World Wars, and foreigners were frequently viewed with a great deal of suspicion. Major Despard is the one who calls Shaitana a dago, and his title indicates military experience.