The Big Four

• Read: 6 Sep 2026 - 10 Sep 2026

• Author: Agatha Christie

• Year: 1927

• Pages: 228

• Remarks: Hercule Poirot Series Book 5

• Synopsis:

  • After an unexpected reunion in London, Hercule Poirot and Captain Arthur Hastings were thrust into a global mystery following the frantic arrival of a dying agent who revealed the existence of an international criminal syndicate. This shadowy organisation, known as The Big Four, combined Eastern intellect, American wealth, French scientific expertise, and deadly execution in a bid for world domination. As mysterious murders and kidnappings unfolded across Europe, Poirot and Hastings were forced to match wits with these ruthless masterminds in their most perilous investigation yet.

[10 Sep 2026] ‘The Big Four’ (1927), by Agatha Christie.

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Reading Background:

• Read this book right on the heels of 'The Murder of Roger Ackroyd', because that book made me so fond of the Hercule Poirot Series. 

• During this HL period, I have established a routine where I wake up at my usual time for work, then go swimming and walking, before returning to do physio and other strengthening exercises, and spending most of my remaining time reading.

What I enjoyed about the book:

• The international espionage thriller elements. 

  • This book departed from Christie's usual mystery crime formula, where a crime takes place in a closed setting among a specific group of people, and Poirot solves the case by identifying the perpetrator from within that group.

  • Instead, it introduced a significant thriller element set on an international stage. It felt epic, and I was hooked by the plot right from the start!

• The dynamics of the Poirot-Hastings friendship.

  • This book also marked the return of Hastings. I had strongly disliked his appearances in previous books because Christie wrote him as rather dense, which frustrated me greatly.

  • While he was still somewhat obtuse here, I was quite moved by the loyalty and brotherly love that he and Poirot share. The scenes where they were willing to sacrifice for each other, or where they realised the depth of their mutual loyalty, were heart-warming and wholesome.

What I found less enjoyable about the book:

• The awkward pacing.

  • As I read the book, I  found the pacing quite strange. The first few chapters were fast-paced and thrilling, but the momentum stalled and became rather tedious and in the middle.

  • Additionally, almost every chapter seemed to end with a mini-resolution to a mystery, which felt repetitive and jarring. 

  • It was only whilst writing this review that I discovered the book was originally a series of 12 short stories, which Christie hastily stitched together to meet a contractual deadline.

• The unsatisfactory ending.

  • The ending felt too rushed and sudden. The build-up was excellent, like I was eagerly anticipating the final showdown between Poirot/Hastings and the criminals, but it turned out to be fleeting and rather anti-climatic.

  • Knowing now that the book was a rushed patchwork to meet a deadline explains this unsatisfactory conclusion. 

My overall thoughts:

• I felt that this book had so much potential. I was highly intrigued by the first few chapters. They were thrilling and the scenes felt like those in international espionage films of 'James Bond' or 'Mission: Impossible'. There was a sense of novelty, seeing it deviate from Christie's traditional closed-room mystery style in her previous Hercule Poirot books. 

• Ultimately, the strange pacing and unsatisfactory ending were its greatest weaknesses in my view, and these were the result of Christie stitching 12 short stories together in a rush to meet a publication deadline (whilst also dealing with the personal crises of her mother's death and her husband's request for a divorce).

• This book was slightly above average for me, despite Christie herself describing it as "rotten". I am still looking forward to reading more from the Hercule Poirot Series!   

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• Chapter 1: The Unexpected Guest

  • Captain Arthur Hastings returned to England after spending eighteen months on a ranch in Argentina. Upon arriving in London, he proceeded directly to 14 Farraway Street to surprise his old friend, Hercule Poirot. To his astonishment, Hastings found Poirot packing his luggage in preparation for an immediate departure to Rio de Janeiro. Poirot explained that Abe Ryland, the American soap tycoon and reputed richest man in the world, had offered him a colossal fee to investigate financial irregularities in South America. Although reluctant to take a long sea voyage, Poirot had accepted the offer, partly to join Hastings in South America. Before his departure, Poirot mentioned that his attention had recently been drawn to a shadowy international network known as The Big Four. Suddenly, an uninvited visitor covered in dust and mud fumbled at the bedroom door, staggered into the room, and collapsed onto the floor. The man appeared deeply traumatised and repeated Poirot's address mechanically. Dr Ridgeway was summoned, and when given paper, the visitor repeatedly scrawled the numeral 4. When Hastings casually uttered the phrase The Big Four, the man suddenly revived and declared that Mandarin Li Chang Yen represented Number 1 and the controlling brain, Number 2 represented American financial power symbolised by a dollar sign, Number 3 was a Frenchwoman, and Number 4 was the ruthless executive known as the Destroyer. The man then fainted. Realising that a grand international conspiracy was at hand, Poirot abandoned his voyage to South America, jumped off his held-up train at Woking, and returned with Hastings to London.

• Chapter 2: The Man From The Asylum

  • Upon returning to London by motor car, Poirot explained to Hastings that his lucrative offer in South America had been a clever ploy engineered by The Big Four to remove him from England. When they entered the flat, they discovered that the mysterious intruder had been killed in their absence. Shortly afterwards, a burly man wearing a uniform arrived, claiming to be an attendant from Hanwell Asylum. He asserted that the deceased was an escaped inmate suffering from severe persecution mania concerning Chinese secret societies, and he formally identified the body. Inspector Japp subsequently arrived and recognised the corpse as Mayerling, a brilliant Secret Service officer who had vanished in Russia five years previously. Poirot conducted a careful examination and deduced that Mayerling had been gagged and murdered with concentrated prussic acid fumes, after which the assassin had opened all the windows to clear the scent of bitter almonds. Poirot also discovered that an eight-day mantelpiece clock had been stopped deliberately at 4 o'clock, serving as a grim signature of Number 4. Poirot telephoned Hanwell Asylum and learned that no patient had escaped, proving that the fake attendant was actually Number 4 in disguise. Poirot acknowledged that he and Hastings were now engaged in a deadly duel with The Big Four.

• Chapter 3: We Hear More About Li Chang Yen

  • Seeking further information regarding Chinese clandestine networks, Poirot and Hastings visited Mr John Ingles, a retired civil servant residing in a southern London suburb. Ingles revealed that Mandarin Li Chang Yen was the mastermind behind worldwide labour unrest, political revolutions, and civil upheavals, functioning as the hidden force behind prominent figures in Russia. He explained that four individuals who had attempted to oppose Li Chang Yen over the preceding four years had all died under suspicious circumstances, including stabbing, poisoning, cholera, and severe electrical burns. Furthermore, a young Chinese chemist who had fled Li Chang Yen's palace after witnessing horrifying experiments on human coolies was killed when Ingles's residence was mysteriously burned down. Ingles presented a letter from Jonathan Whalley, a retired seafaring man living at Granite Bungalow in Hoppaton, Dartmoor, requesting financial assistance because The Big Four were pursuing him. Poirot, Hastings, and Ingles travelled immediately to Dartmoor, only to discover upon arrival that Whalley had been murdered earlier that day, his throat cut from ear to ear and his valuable Chinese jade figures stolen. Local Inspector Meadows had arrested Whalley's servant, Robert Grant, an ex-convict whose bloodstained boots matched the footprints left between the body and Grant's room, where the stolen jade had been hidden.

• Chapter 4: The Importance Of A Leg Of Mutton

  • Poirot, Hastings, and Ingles inspected the crime scene at Granite Bungalow. Poirot observed that Grant's bloodstained footprints led from the kitchen to the living room, returned to the kitchen, and then re-entered the living room a second time before retreating to Grant's bedroom. While exploring the larder, Poirot discovered a frozen leg of mutton. As the murder occurred on a Monday, Poirot deduced that the imported meat must have been delivered that morning by a butcher's cart, despite local assertions that no strangers had visited the bungalow. Poirot interviewed Grant in police custody at Moreton. Grant maintained his innocence regarding the murder, confessing that he had entered the room, found his master already dead, panicked because of his criminal record, yielded to temptation by stealing the jade figures, and prepared to flee before the housekeeper raised the alarm. Grant revealed that he had secured his post through a prisoners' relief worker named Saunders, who walked with a limp, possessed a broken front tooth, wore spectacles, and had given Grant a pair of boots. Poirot realised that Number 4 had disguised himself as a butcher's delivery man, driven to the bungalow in a butcher's cart, worn a duplicate pair of boots provided to Grant, murdered Whalley to acquire his secrets, framed Grant by leaving bloodstained prints, and departed unnoticed in broad daylight.

• Chapter 5: Disappearance Of A Scientist

  • Following Poirot's testimony at the trial, Robert Grant was acquitted of the murder of Jonathan Whalley after evidence proved that a fake butcher's cart had visited Granite Bungalow on that Monday morning. Back in London, Inspector Japp introduced Poirot to Captain Kent of the United States Secret Service. Kent explained that seized documents revealed that the mysterious destruction of several American warships off the coast had been caused by a secret, focused wireless energy beam controlled by The Big Four rather than a natural tidal wave. Kent had come to England to consult John Halliday, a brilliant young British scientist who was the leading authority on wireless energy beam technology. Japp disclosed that Halliday had mysteriously vanished in Paris two months earlier following a brief disagreement with his wife. Poirot and Hastings visited Mrs Halliday and her young daughter at Chetwynd Lodge near Chobham, Surrey. Mrs Halliday insisted that her husband was entirely devoted to his scientific research and would never voluntarily abandon his family. She provided his Paris itinerary, noting that he had met Professor Bourgoneau and the renowned French scientist Madame Olivier at Passy before disappearing from his hotel on Saturday 22 July. Poirot resolved to travel to Paris immediately to solve the mystery.

• Chapter 6: The Woman On The Stairs

  • Poirot and Hastings travelled to Paris to investigate John Halliday's disappearance. They visited Madame Olivier at her villa in Passy, where she was conducting pioneering research on gamma rays from Radium C and magnetical phenomena. During their interview, Poirot observed a woman dressed in dark widow's mourning enter the villa and hurry upstairs without looking at the visitors, which struck him as unnaturally suspicious. As Poirot and Hastings departed, a large tree branch crashed down onto the pavement, narrowly missing them, which Poirot recognised as a deliberate attempt on their lives by their enemies. Poirot deduced that Halliday had been intercepted outside the villa by the widow, lured into an adjoining property, and captured. Returning to the villa, Poirot confronted the widow, who unmasked herself as Countess Vera Rossakoff, an old acquaintance from London who was operating as Madame Olivier's secretary under the name Inez Veroneau. Countess Rossakoff struck a bargain with Poirot, telephoning her accomplices to release Halliday at his hotel in exchange for her own freedom. Although Halliday was safely restored to his hotel room and reunited with his wife, he was so utterly terrified by the brutal threats of The Big Four against his family that he refused to divulge any details regarding his captivity or his scientific discoveries.

• Chapter 7: The Radium Thieves

  • While remaining in Paris, Poirot and Hastings were visited in their hotel room by a tall, sallow man with a hooked nose who claimed to represent The Big Four. The visitor offered Poirot a bribe of one hundred thousand francs if he would abandon his investigation and return to private cases in London, threatening him with death if he refused. Hastings attempted to overpower the intruder, but the man utilised a Japanese martial art technique to throw Hastings against the wall and escaped, disguising himself as an hotel waiter. In his hurry, the intruder dropped a brown leather pocketbook containing a note appointing a Big Four meeting at 34 Rue Des Echelles at 11:00 am. Poirot recognised the note as a decoy trap and avoided it. Shortly afterwards, Madame Olivier summoned Poirot to Passy, reporting that her laboratory had been broken into and valuable research papers stolen, although the thieves had failed to breach the safe containing millions of francs worth of radium. Poirot arranged a fake departure for England by train, pulling the communication cord outside Paris with the aid of his friend Pierre Combeau to alight unnoticed. Disguised as labourers, Poirot and Hastings returned to the villa at night, where they were ambushed in the garden by ten men, bound, and taken into a secret subterranean chamber beneath the laboratory. Madame Olivier unmasked herself as Number 3 of The Big Four and prepared to execute them. Poirot outwitted her by claiming that his cigarette contained a South American curare blowpipe device, forcing her to untie Hastings, who then bound Madame Olivier and liberated Poirot.

• Chapter 8: In The House Of The Enemy

  • Returning to London, Poirot received a curt letter from American multimillionaire Abe Ryland, who expressed severe displeasure at Poirot's abrupt cancellation of his South American assignment. Remembering Mayerling's deathbed revelation that Number 2 was an American representing vast financial wealth, Poirot suspected Ryland of being Number 2 of The Big Four. Poirot arranged for Hastings to be transformed by a professional makeup artist into Arthur Neville, an English secretary, utilising height-increasing shoes, cheek pads, an altered hairline, and a gold tooth. Disguised as Neville, Hastings obtained a secretarial post with Ryland at the Savoy and accompanied him to Hatton Chase, an estate rented from the Duke of Loamshire. After three weeks, Ryland's stenographer, Miss Martin, informed Hastings that Ryland had flown into a rage when she accidentally opened a letter written on blue paper marked with a small numeral 4. The letter contained a coded message ("Essential should see you quarry seventeen eleven four"), indicating a meeting at a disused quarry on 17 October at 11:00 pm. Hastings communicated the finding to Poirot and hid in the quarry at the designated time, but he was captured by Ryland and his valet Deaves. Ryland threatened to kill both Hastings and Poirot in a simulated landslide, but Poirot arrived with a force of Scotland Yard officers and surrounded the quarry. Although Ryland subsequently claimed to Inspector Japp that the incident was merely a foolish prank arranged by his footman James on a wager, Poirot recognised that James the footman was Number 4 in disguise and that Ryland was indeed Number 2.

• Chapter 9: The Yellow Jasmine Mystery

  • A month after the events at Hatton Chase, Inspector Japp invited Poirot and Hastings to Market Handford in Worcestershire to investigate the mysterious death of Mr Paynter. Paynter, a wealthy fifty-five-year-old bachelor and globe-trotter who had purchased Croftlands, resided with his artist nephew Gerald Paynter and a Chinese servant named Ah Ling. Paynter became ill after eating curry at dinner, summoned Dr Quentin (a locum standing in for Dr Bolitho), and handed over his uneaten curry for analysis, suspecting foul play. Dr Quentin administered a hypodermic injection of what he described as strychnine to support Paynter's heart, but the following morning Paynter was found dead with his head charred to a cinder in his study fireplace, and the door locked from the inside. Before dying, Paynter had dipped his finger in ink and scrawled the words Yellow Jasmine across a newspaper, together with two lines forming the beginning of the numeral 4. Analysis revealed that the curry contained a lethal quantity of powdered opium, placing suspicion upon Ah Ling. Poirot tested Ah Ling by drawing the numeral 4 in table dust, causing the servant to display sudden terror, which confirmed the involvement of The Big Four. Poirot researched yellow jasmine (Gelsemium) and realised that Dr Quentin had poisoned Paynter with a fatal injection of gelseminine rather than strychnine, unlatched the window, and returned during the night to steal Paynter's completed manuscript, titled The Hidden Hand In China, before pushing his corpse into the fire to conceal the cause of death. Poirot deduced that Dr Quentin was Number 4 in disguise, who escaped before police could apprehend him.

• Chapter 10: We Investigate At Croftlands

  • Poirot, Hastings, and Inspector Japp conducted a thorough examination of the study at Croftlands, inspecting the locked door, the unlatched garden window, and the surrounding footprints. Japp confirmed that Paynter's completed manuscript, The Hidden Hand In China, had vanished from the house, providing clear evidence of a Big Four conspiracy to suppress vital information regarding Li Chang Yen. Poirot questioned Gerald Paynter, who detailed his arrival home at 11:00 pm and explained his long separation from his uncle prior to answering a legal advertisement. Poirot and Hastings visited Dr Quentin's surgery, where Quentin discussed psychological memory phenomena and claimed he could not recall whether the garden window had been latched. Poirot evaluated both Ah Ling and Gerald Paynter, initially considering whether Gerald was an impersonator deployed by Number 4. After purchasing a medical botanical text in Market Handford and discovering the paralytic properties of yellow jasmine, Poirot reconstructed how the fake Dr Quentin had added opium to the curry after taking it from the house to frame Ah Ling, while administering yellow jasmine directly to Paynter. Despite Poirot's deductions, the fake Dr Quentin escaped after sending a telegram to recall Dr Bolitho from his holiday, leaving Poirot to trace the numeral 4 on the table in frustration.

• Chapter 11: A Chess Problem

  • Poirot, Hastings, and Inspector Japp dined at a Soho restaurant, where Japp discussed the sudden death of young American chess prodigy Gilmour Wilson during a match against Russian champion Dr Savaronoff. Savaronoff, who had escaped Siberian exile after the Russian Revolution, lived as a recluse in Westminster with his niece Sonia Daviloff and a wooden-faced servant named Ivan. Wilson had collapsed dead while making his third move in the match held at Savaronoff's flat, yet an autopsy revealed no trace of poison or heart disease, only a small burn mark on his left hand. Poirot visited the mortuary, noted that Wilson was left-handed, and retrieved a carved ivory white bishop piece clasped in Wilson's hand. Poirot and Hastings visited Savaronoff's flat, where Poirot noticed a small hole in a Persian rug and was confronted by Sonia Daviloff, who expressed fear that her uncle was being targeted by The Big Four. Poirot interviewed Dr Savaronoff on his couch, learning that Wilson had opened the game with the Ruy Lopez opening. After weighing two duplicate white bishop pieces, Poirot discovered one contained a concealed metal rod designed to deliver a lethal electric shock when placed on a metal square of a specially wired table connected to the flat below. Poirot realised that Dr Savaronoff was actually Number 4 in disguise, who had killed Wilson to prevent the American champion from discovering that the imposter could not play chess at all. Number 4 escaped before police arrived, sending Ivan away and leaving Sonia Daviloff chloroformed in the flat.

• Chapter 12: The Baited Trap

  • In mid-January, six months after Hastings's return to England, Hastings received a fake cablegram from South America claiming his wife Cinderella had been kidnapped by The Big Four. A Chinese messenger arrived at 14 Farraway Street with a note demanding that Hastings follow him immediately without informing Poirot or Cinderella would suffer. Before leaving, Hastings dropped four books onto the floor and spilled four knobs of coal into the grate as a secret signal for Poirot. Hastings was led through Chinatown to a subterranean oriental palace, where a Chinese deputy of Li Chang Yen threatened to throw Hastings into an underground river unless he wrote a letter to decoy Poirot into a trap. Hastings refused, but when the deputy threatened Cinderella with slow torture, Hastings yielded and allowed the deputy to dictate a clever decoy letter to Poirot. Hastings was taken to a ground-floor house in Chinatown to call Poirot inside when he arrived, but at the crucial moment, Hastings shouted a warning to Poirot to stay back. Poirot detonated a special poison gas bomb invented by a chemist friend, rendering the Chinese gang unconscious, while wearing a gas mask hidden under a yellow muffler. Scotland Yard officers rushed in and rescued Hastings, after which Poirot revealed that he had anticipated such a move and had moved Hastings's wife Cinderella to a safe location three months earlier, rendering the kidnapping threat entirely false.

• Chapter 13: The Mouse Walks In

  • Hastings recounted his ordeal in the Chinatown cellar to Poirot, detailing the psychological pressure and the threat of the river opening. Poirot praised Hastings's bravery and cleverness in leaving the clues of the four books and four knobs of coal at the flat. Poirot explained that his moustaches had allowed him to easily conceal a respirator under his yellow muffler during the gas bomb attack. Hastings expressed terror for Cinderella's safety in South America, but Poirot reassured him that the cablegram was a complete forgery sent by Big Four operatives. Poirot revealed that he had quietly arranged for Cinderella's protection months prior, housing her in a secret location to prevent The Big Four from using her as leverage. Hastings was deeply moved by Poirot's foresight and devotion to his friend's family. Poirot reaffirmed his determination to crush The Big Four once and for all.

• Chapter 14: The Peroxide Blonde

  • Although four Chinese gang members were arrested during the Chinatown raid, the leader escaped through hidden underground passages. Poirot searched the Chinatown premises and found detailed dossier notes compiled by The Big Four regarding Hastings's and Poirot's characters, strengths, and weaknesses. Poirot analysed the identity of Number 4, establishing that he was an actor between thirty and thirty-five years of age, of medium height and fair colouring, adept at character roles, and lacking natural teeth. Poirot employed private detective Joseph Aarons and solicitors McNeil and Hodgson to narrow down a list of missing actors to four names: Ernest Luttrell, John St Maur, Austen Lee, and Claud Darrell. A retired actress named Flossie Monro responded to an advertisement regarding Claud Darrell and met Poirot and Hastings for lunch at an expensive restaurant. Flossie described Darrell's distinctive habit at the dinner table of dabbing bread crumbs with a small piece of bread between his fingers. Flossie promised to send Poirot an old photograph of Claud Darrell from her flat, but as she returned home, she was deliberately run down and killed by an automobile driven by a Big Four agent who stole her latchkey. Poirot and Hastings rushed to Flossie's flat, only to find it ransacked and an empty photograph frame marked with a new price label left behind by Number 4 as a taunting gesture.

• Chapter 15: The Terrible Catastrophe

  • In late March, Poirot's nerve appeared shaken, and he spent large sums paying mysterious Russian contacts while keeping his plans secret from Hastings. Poirot arranged a high-level conference with Home Secretary Sydney Crowther and French Premier M. Desjardeaux to warn them of The Big Four's global plot and Madame Olivier's involvement. Desjardeaux was incredulous regarding Madame Olivier, but Mr John Ingles supported Poirot's claims regarding Li Chang Yen's supreme intellect. Poirot handed Crowther a sealed envelope and key to a safe deposit containing his complete files on The Big Four, to be opened in the event of his death. Poirot mentioned that he possessed a twin brother named Achille Poirot, who lived near Spa in Belgium, lacked moustaches, and possessed equal deductive abilities. A hospital nurse named Mabel Palmer called on Poirot, reporting that her patient, Mr Templeton of Hertfordshire, was suffering from gastric attacks and believed "the four of them" were trying to poison him. Analysis revealed antimony in Templeton's soup, prompting Poirot and Hastings to travel to Elmstead, where they met Mrs Templeton, Dr Treves, and Templeton's dull-witted son Micky. During dinner, Micky exhibited Claud Darrell's habit of dabbing breadcrumbs, revealing to Poirot that Micky was Number 4 in disguise. Poirot and Hastings escaped down an ivy vine to catch a train back to London, but upon entering their flat, Poirot tried to stop Hastings from lighting the fire, causing a rigged booby-trap matchbox to explode. Hastings regained consciousness twenty-four hours later in Dr Ridgeway's surgery, where Ridgeway informed him that Hercule Poirot had perished in the explosion.

• Chapter 16: The Dying Chinaman

  • Devastated by Poirot's death, Hastings vowed to avenge his friend and continue his work against The Big Four despite Dr Ridgeway's pleas for him to return to South America. Hastings attended Poirot's funeral, which was attended by numerous dignitaries and featured a massive wreath of crimson roses sent by Countess Rossakoff. In May, Hastings advertised for information on Claud Darrell and was approached in a Soho restaurant by a dark-bearded man who arranged salt into four heaps on Hastings's plate, identifying himself as Number 4 and warning Hastings to leave England. Ten days later in Hyde Park, Countess Rossakoff met Hastings in her limousine and issued a second warning that the third warning would come from the Destroyer. St Giles's Hospital telephoned Hastings regarding a dying Chinaman who had been knifed in the docks with Hastings's address in his pocket; the man was John Ingles's servant. Before dying, the Chinaman whispered the words hand, Largo, carrozza, and Cara Zia to Hastings. Returning home, Hastings received a posthumous letter from Poirot instructing him to return to South America immediately as part of Poirot's master plan. Hastings boarded the S.S. Ansonia for Buenos Aires, receiving a final note from Number 4 stating "You are wise", but in mid-ocean, a Royal Navy destroyer intercepted the liner under Admiralty orders, replaced Hastings with an actor, and landed Hastings secretly on the Belgian coast. Hastings was driven into the Ardennes to a secluded white villa near Spa, where he was astonished to find Hercule Poirot alive and well. Poirot revealed that his death had been faked with Dr Ridgeway's help to convince The Big Four that their greatest enemy was dead, allowing Poirot to prepare his final counter-offensive in total secrecy.

• Chapter 17: Number Four Wins A Trick

  • Poirot explained that the dying Chinaman's words pointed to the Big Four's headquarters at Karersee (Lago di Carezza) in the Italian Dolomites (Cara Zia being a phonetic rendering of Carezza, carrozza referring to the carriage or drive, and Largo referring to the lake). Intelligence officer Captain Harvey arrived at the villa in late June, reporting that Li Chang Yen had isolated China, while Abe Ryland and Madame Olivier had departed for Italy. Poirot, Hastings, and Harvey travelled to Bolzano and drove up to the mountain resort of Karersee in the Dolomites, where Ryland's quarrying company served as a front for a vast subterranean fortress inside the mountain. At the hotel dining room, Poirot observed a pasty-faced man at the adjacent table dabbing breadcrumbs, identifying him as Number 4. On the hotel terrace, Number 4 joined Poirot and Hastings, lit a match, and plunged the terrace into darkness while breaking a bulb of ethyl chloride, rendering Poirot and Hastings unconscious. Accomplices gagged Poirot and Hastings and dragged them through the hotel basement into the forest towards the Felsenlabyrinth.

• Chapter 18: In The Felsenlabyrinth

  • Poirot and Hastings were carried through a secret rock door in the Felsenlabyrinth into the subterranean mountain fortress of The Big Four. They were brought before the leaders of The Big Four: Abe Ryland (Number 2), Madame Olivier (Number 3), Number 4, and the empty draped chair of Li Chang Yen (Number 1). Countess Vera Rossakoff entered and recognised that the captured man was not Hercule Poirot; she tore off his false moustaches, revealing a scarred upper lip and identifying him as Achille Poirot, Hercule's twin brother. Achille Poirot announced that Hercule Poirot was outside leading an armed force of international detectives and soldiers surrounding the mountain, guided by aniseed trails left on Achille's boots. Realising defeat was imminent, Madame Olivier and the leaders chose to detonate the subterranean fortress using atomic explosives to destroy themselves and their enemies together. Left alone with Countess Rossakoff, Achille bargained for their escape by offering to restore her lost child to her, showing her a photograph of her son whom Hercule had located and saved from starvation in Russia. Countess Rossakoff guided Achille and Hastings through secret mountain tunnels, emerging into the morning light just as a colossal explosion shattered the mountain, destroying the fortress and killing Ryland, Madame Olivier, and Number 4. In the aftermath, Achille revealed himself to be Hercule Poirot all along, having adopted the persona of Achille with shaved moustaches, belladonna, and a real scar to deceive Number 4 completely. News arrived that Li Chang Yen had committed suicide in China following the collapse of his revolution, marking the total defeat of The Big Four, after which Poirot announced his intention to retire to cultivate vegetable marrows.