'And Then There Were None' (1939) is widely considered Agatha Christie's bestselling novel and one of the bestselling crime novels of all time, with over 100 million copies sold. Its innovative plot structure, isolated setting, and psychological tension have made it a masterpiece of the crime genre. While 'Murder on the Orient Express' and 'ABC Murders' are also highly acclaimed, 'And Then There Were None' remains her most commercially successful work.