"The Murder of Roger Ackroyd" (1926): This novel is often considered one of Christie's greatest masterpieces. It introduces another iconic detective, the village doctor and amateur sleuth, Dr. Sheppard. When a wealthy widower named Roger Ackroyd is found dead, Dr. Sheppard becomes embroiled in the investigation. The novel is renowned for its audacious twist ending, which shocked readers and cemented Christie's reputation as a master of deception.
