I’m always surprised at your ignorance of common day things. Most Americans would know who Agatha Christie was, even if they don’t know what an Agatha Christie is.
Agatha Christie is a very famous mystery writer, she wrote Murder on the Orient Express and Death on the Nile. You must have heard of those surely.
She popularised the whodunnit, where the murderer is revealed at the end and the reader has to see if they can work it out beforehand.