The story begins when a dusty, terrified stranger stumbles into Poirot's bedroom and scrawls the number "4" repeatedly before collapsing. This dying clue pulls Poirot and his loyal friend, Captain Arthur Hastings, into a high-stakes global conspiracy. They learn about a ruthless criminal syndicate known as the Big Four, which aims to destroy world order and seize global economic control.
The syndicate is led by four powerful masterminds: Number One is Li Chang Yen, a Chinese political mastermind; Number Two is Abe Ryland, an American millionaire; Number Three is Madame Olivier, a French scientist; and Number Four is an elusive English master of disguise known as the Destroyer. To fight this deadly quartet, Poirot fakes his own death to work in secret. He and Hastings track the villains across multiple international encounters before trapping the remaining members in an Italian mountain hideout. The cartel is ultimately destroyed in a massive explosion, allowing Poirot to emerge from hiding and restore safety.
