The world stands on the edge of an abyss as the outbreak of World War II grows ever closer... In an effort to demonstrate international unity, the 'Peace Party' hosts a grand reception, which re-unites POIROT with his good friend JAPP, now Assistant Commissioner of the Met. The illustrious crowd also includes English diplomat STEPHEN PAYNTER, and the French scientist and Peace Party stalwart, MADAME OLIVIER. The American tycoon, and hearty backer of the Party, ABE RYLAND, fronts the event, which climaxes in an exciting game of chess, where he takes on the reclusive Russian Grandmaster, DR. IVAN SAVARANOFF. But the match has barely begun, when suddenly SAVARANOFF collapses - dead! Panic quickly spreads when RYLAND suspiciously disappears. Daily Comet journalist, TYSOE, covers every development in great, sensational detail, claiming the murder to be the work of a group of ruthless political agitators, tagged as the "the Big Four". Then when JONATHAN WHALLEY, the biographer of the Peace Party's Chinese leader, is also strangely and brutally murdered, the Big Four have the attention of HERCULE POIROT and the world. TYSOE is keen to join forces with POIROT - an anonymous source has been feeding the journalist information on the Big Four - apparently a mole from within. POIROT and JAPP decide to pool resources with him when it appears that his informer is murdered - leaving behind evidence which suggests that this dissident and dangerous group is in fact none other than the Peace Party! A theory only reinforced by the disappearances of RYLAND and then MADAME OLIVIER, shortly after the murder of unassuming conciliator PAYNTER. POIROT realises that each of these crimes is so dramatic and expertly stage-managed as to be almost theatrical... and the murderer must indeed be a master of disguise in order to pull off all of such varied and ingenious plans. Through a scrapbook found at WHALLEY's house, he tracks down failing actress FLOSSIE MONRO, whom he believes may unwittingly be at the root of all this bloodshed. However, before he can pursue his theories - POIROT himself is also killed! Or is he..? CAPTAIN HASTINGS and MISS LEMON return for the funeral of their old friend, but of course things are never as they seem, and soon the theatrics of the Big Four climax with a deadly final act - but on whom will the curtain fall this time..?