Belgium sleuth Hercule Poirot untangles a baffling mystery of a murderer who announces his next victims through a series of letters each addressed to the detective himself. After a stay at the Ritz in Paris, Poirot is flying home to London when a fellow passenger succumbs mysteriously. A ruthless blackmailer is killed on board a plane full of likely suspects. Unfortunately for the culprit, Belgium sleuth Hercule Poirot is also on board. While recovering from a war wound, Hastings meets Poirot and solve the murder at the Styles. Poirot must solve the murder of his dentist where a broken shoe buckle becomes the key to solving the crime. While staying at End House in Cornwall, Poirot must solve the mysterious attempts to kill Nick Buckley.