Question: How many novels did the detective who helped Antoinette Marceau on the Murder on the Orient Express appear in?
Sentence (from "Agatha Christie: Murder on the Orient Express"): The plot follows an amateur sleuth, Antoinette Marceau, and her investigation of a murder with twelve possible suspects aboard the Orient Express, which has been blocked by an avalanche in the Kingdom of Yugoslavia during 1934.
Relevant evidence: No