Conversation so far:
What were some of Agatha Christie's first novels?
The Mysterious Affair.
Was this book successful?
CANNOTANSWER.
What is Poirot?
a former Belgian police officer noted for his twirly large "magnificent moustaches" and egg-shaped head.
Was Poirot a character in one of her books?
The Mysterious Affair at Styles.

Question: What is another of her first novels?
Self-contained rewrite: Other than The Mysterious Affair, what is another of Agatha Christie first novels?