The Mystery of the Blue Train

• Read: 11 Sep 2026 - 15 Sep 2026

• Author: Agatha Christie

• Year: 1928

• Pages: 308

• Remarks: Hercule Poirot Series Book 6

• Synopsis:

  • When wealthy American heiress Ruth Kettering was gifted the priceless "Heart of Fire" rubies by her father, she boarded the luxurious Blue Train to the French Riviera amidst a turbulent personal life. Tragedy struck during the overnight journey when Ruth was found murdered in her carriage and her valuable jewels were stolen, casting suspicion on a varied group of passengers. Renowned Belgian detective Hercule Poirot, who happened to be travelling on the same train, agreed to investigate the horrific crime and unmask the cunning culprit.

[15 Sep 2026] ‘The Mystery of the Blue Train’ (1928), by Agatha Christie.

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Reading Background:

• Started this book on the heels of finishing 'The Big Four'. Initially, I had thought that I would move on to read another series, but it seems that for the time being I am rather charmed by the Hercule Poirot Series!

• Forgot to mention that on 6 Sep 2026, the National Library Board (NLB) launched the ReadSG Challenge on CrowdTask SG. G and I have been logging in daily to log how much time we have spent reading. Each reading log has earned us 20 coins, which translates to SGD0.02 haha. Apparently, foreign news articles have been reported about this initiative in Singapore, where we are monetarily incentivised to read! Of course, one could just untruthfully create a reading log without actually reading anything, but still, it's quite an interesting initiative and suits us bookworms very well.

What I enjoyed about the book:

• The writing style.

  • Christie's writing felt different in this book compared to her previous few. Even though they were all crime or murder mystery books, Christie's writing used to feel somewhat light-hearted and bouncy, sometimes to the point of being comical.

  • In this book, however, things felt darker and more serious, and the prose felt more mature. It was a refreshing change from her previous books.

• The thrill and intrigue.

  • As I was reading the book, every scene played like a mystery thriller film in my head.

  • I liked how there was a prelude in this book, which was intriguing and mysterious. I also liked how there was proper suspense built up all the way till the train ride before the murder took place, and that was thrilling! 

What I found less enjoyable about the book:

• The superficial red herrings.

  • I don't know why Christie wrote it in such a way where initially there were so many potential suspects, but then in the second half of the book, she suddenly narrowed down for readers on who the perpetrators might be. 

  • Even worse, between the potential perpetrators, she kept trying to point to somebody as the murderer. It wasn't even subtle. Obviously, readers could then easily guess who the culprit was. It felt rather anti-climatic.

• The hugely untapped potential.

  • This book developed so much backstory for many of its characters in the first half of the book, such that readers would actually grow attached to them. Alas, I felt that they were just unsatisfactorily abandoned at the end. 

My overall thoughts:

• Honestly, I quite liked this book, despite reading online after I had finished the book that Christie herself hated it. 

• I was so intrigued by the mystery, suspense, and thrill of the story, especially in the first half! I also liked the new writing style, which I felt refreshingly different from that of the previous books, in the way the style of 'Harry Potter and the Goblet of Fire' felt different from the first 3 books of its series. However, I am now wondering whether the darker and more serious tone were the effects of the personal crisis she was facing whilst writing this book.

• I was a little pissed by how easy it was to guess who the murderer was though, because of Christie's sloppy treatment of the red herrings. I also lamented the fact that so many characters were developed well, but were just discarded at the end. Especially Katherine Grey, I had grown so attached to her, only to find out disappointingly that she wouldn't appear in any following books. Zzz.

• All in all, an above-average book for me! Still charmed by the series. On to the next Poirot book!

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• Chapter 1: The Man With The White Hair

  • Late at night in Paris, Boris Krassnine, a weak-looking Russian political operative, walked through a dilapidated quarter to the apartment of Olga Demiroff. Sensing that they were under surveillance by two apaches and a mysterious white-haired man, Krassnine retrieved a concealed parcel from beneath the coals in the fireplace. An American buyer arrived, inspected the contents—which were valuable rubies—paid for them in banknotes, and departed into the night. Krassnine and Olga watched from the window as the American walked away unharmed, with Olga remarking that the American would survive because he was clever, and predicting that he would eventually give the jewels to a woman.

• Chapter 2: M. Le Marquis

  • The white-haired man strolled through the streets of Paris and learned that the American buyer had repelled an attack by the two apaches by firing shots from a revolver. Unbothered by the failure of the ambush, the man proceeded to the secluded antique shop of D. Papopolous. Donning a black satin mask, he introduced himself as M. le Marquis and met the venerable dealer. The two men discussed their secret plot to obtain the rubies without relying on crude direct attacks. After M. le Marquis departed, Papopolous’s daughter, Zia, who had listened at the keyhole, observed that the visitor was an Englishman who spoke French fluently and wore a wig.

• Chapter 3: Heart Of Fire

  • In London, American millionaire Rufus Van Aldin returned to his suite at the Savoy Hotel, where his secretary, Major Richard Knighton, was sorting mail. Knighton was a disabled English war veteran whom Van Aldin had hired two months earlier. Van Aldin opened a letter from his daughter, Ruth Kettering, who was deeply unhappy with her husband, Derek. Van Aldin revealed a red velvet case containing a set of historic Russian rubies he had secretly purchased in Paris, centered around a legendary, flawless gem known as Heart Of Fire, which was intended as a surprise gift for Ruth.

• Chapter 4: On Curzon Street

  • Van Aldin visited Ruth at her town house on Curzon Street, where she expressed outrage over Derek’s public affair with a famous dancer named Mirelle. Van Aldin urged Ruth to cut her losses and file for divorce. Although Ruth hesitated over the potential public scandal, she accepted her father's advice. Van Aldin presented her with the Heart Of Fire rubies, warning her not to take them abroad on her upcoming trip to the Riviera on 14 February, but to leave them safely at a bank. Before departing, Van Aldin instructed Knighton to hire a private investigator named Mr. Goby and to schedule an interview with Derek Kettering.

• Chapter 5: A Useful Gentleman

  • Mr. Goby met Van Aldin early the following morning and was commissioned to gather evidence regarding Derek Kettering's financial troubles and personal conduct. Later, Derek arrived for his interview with Van Aldin, maintaining an ironic and detached attitude while suggesting that Ruth wait until his ailing father died so she could become Lady Leconbury. Van Aldin rejected his cynicism and declared that Derek had married Ruth solely for her money, while Derek countered that Ruth was as hard as granite. Afterward, Goby returned with damning reports confirming Derek's heavy debts and infidelity. Van Aldin then revisited Ruth, who confessed that she had resumed seeing her former lover, the Comte de la Roche, a notorious French swindler whom Van Aldin had forced out of her life years earlier.

• Chapter 6: Mirelle

  • After his tense meeting with Van Aldin, Derek Kettering collided in the Savoy corridor with a grey-eyed woman named Katherine Grey. He then visited Mirelle at her flat, where she was reclining on a divan discussing her artistic career. When Derek informed her that Van Aldin was pushing for a divorce, Mirelle bluntly stated that she would not remain with him if he became penniless. She noted that Ruth’s death would solve his financial problems by making him the heir to two million pounds, and revealed that Ruth was planning to meet the Comte de la Roche in Paris on 14 February.

• Chapter 7: Letters

  • In the village of St. Mary Mead, Katherine Grey received two letters that altered her life. The first was an patronising note from Mrs. Samuel Harfield, suggesting that old Mrs. Harfield's recent will was invalid and offering a small gift to avoid court. The second was from a firm of London solicitors, informing Katherine that the deceased woman had been an original shareholder in Courtaulds and had left her an accumulated fortune yielding thousands of pounds a year. Dr. Harrison and his wife congratulated Katherine, who decided to leave the village, travel abroad, and update her wardrobe in London.

• Chapter 8: Lady Tamplin Writes A Letter

  • At Villa Marguerite on the Riviera, Lady Tamplin read a newspaper report about Katherine Grey's windfall. Realising that Katherine was her cousin, Lady Tamplin immediately penned a letter inviting her to stay at her villa, intending to exploit her newfound wealth. In London, Katherine settled matters with the lawyers, arranged a sum of money for the Harfield relatives, and bought several elegant dresses, including a grey and mauve evening gown titled Soupir d'Automne. While booking her train tickets at Thomas Cook & Sons, she noticed Derek Kettering standing nearby and experienced a sudden, chilling premonition of doom.

• Chapter 9: An Offer Refused

  • Derek Kettering booked a single berth on the Blue Train for 14 February under the alias of his servant, Pavett, and observed Katherine Grey making her own reservation for the same journey. Upon returning to his Jermyn Street rooms, Derek was visited by Major Knighton, who delivered an offer from Van Aldin: £100,000 in cash if Derek allowed the divorce to proceed undefended, coupled with a threat of financial ruin if he resisted. Derek refused the bribe and instructed Knighton to tell Van Aldin to go to hell.

• Chapter 10: On The Blue Train

  • On 14 February, Van Aldin saw Ruth off at Victoria Station, noticing her unusual nervousness and anxiety. Boarding the Pullman car, Ruth sat opposite Katherine Grey, and the two women conversed during the journey across the Channel. On the Blue Train from Calais, Ruth invited Katherine into her compartment and confided that she was travelling to meet her former lover, admitting that she was gripped by a feeling of dread. At the Gare de Lyon in Paris, Katherine glimpsed a dark-haired woman pulling her compartment door shut, and later at dinner, Hercule Poirot sat opposite Katherine, remarking light-heartedly that real life could mirror detective fiction. During the night, Katherine stepped into the corridor and saw a man entering what she believed was Ruth's compartment, recognizing him as Derek Kettering.

• Chapter 11: Murder

  • The following morning, as the train neared Nice, the conductor appeared pale and terrified. Upon arrival, Katherine was met by Lady Tamplin's husband, Chubby Evans, but was detained by the Commissary of Police, M. Caux. M. Caux informed her that Ruth Kettering had been found strangled in her berth with her face disfigured by a heavy blow, and that her scarlet morocco jewel case was missing. Poirot joined the investigation, and Katherine accompanied them to identify the body, confirming Ruth's identity by a mole on her wrist. Pierre Michel, the conductor, stated that Ruth had informed him in Paris that her maid had been left behind, ordered a dinner basket, and requested not to be woken early.

• Chapter 12: At The Villa Marguerite

  • Katherine arrived at Villa Marguerite, where Lady Tamplin eagerly attempted to persuade her to write a newspaper article about her encounter with the victim. That evening, Derek Kettering arrived for dinner as a guest of Lenox Tamplin. Katherine wore her new evening dress and sat next to Derek, mentioning that she had seen him on the Blue Train, which caused him visible discomfort. Mid-way through the meal, Derek received an urgent summons from the Prefect of Police and departed to answer their inquiries.

• Chapter 13: Van Aldin Gets A Telegram

  • In foggy London on 15 February, Van Aldin worked alongside Knighton at the Savoy. Knighton mentioned having bumped into Ruth's maid, Ada Mason, at the Ritz in Paris the previous night, where Mason had claimed that Ruth met a friend unexpectedly and sent her to the hotel to await instructions. Shortly afterward, a telegram arrived from the police in Nice announcing Ruth's murder and robbery. Van Aldin and Knighton arranged to travel to France immediately, while Mr. Goby confirmed that both Derek Kettering and Mirelle had travelled on the same train.

• Chapter 14: Ada Mason’s Story

  • Van Aldin and Knighton arrived in Nice and met M. Carrège, the Examining Magistrate, alongside M. Caux and Hercule Poirot. Ada Mason was questioned and testified that at the Gare de Lyon in Paris, Ruth had returned to her carriage with a tall, dark gentleman, shut the door, and then ordered Mason to take her luggage to the Ritz in Paris and wait for a telegram. Mason confirmed that the scarlet morocco case containing the Heart Of Fire rubies had remained with Ruth. M. Carrège then presented a letter found in Ruth's handbag, signed by "Armand" (the Comte de la Roche), arranging a secret meeting at the Isles d'Or.

• Chapter 15: The Comte De La Roche

  • Van Aldin expressed deep anger upon discovering the letter, identifying the Comte de la Roche as an unscrupulous swindler who preyed upon wealthy women. Van Aldin admitted purchasing the Russian crown rubies in Paris ten days earlier, realizing that the Comte had lured Ruth into bringing them along. Poirot reconstructed the crime, proposing that the Comte had hidden in the adjacent compartment, murdered Ruth, taken the jewels, and stepped off the train at Lyons. However, Poirot pointed out a psychological inconsistency, noting that while the Comte was a thief, he was typically too cowardly to commit a violent murder. Poirot then revealed that the Comte was currently staying at Villa Marina in Antibes.

• Chapter 16: Poirot Discusses The Case

  • During further discussions, the authorities noted that Derek Kettering stood to inherit two million pounds from his wife's estate, as she had died without making a will. Van Aldin retained Poirot personally to investigate the murder, detailing Derek's financial ruin and his refusal of the £100,000 offer. Poirot observed that Derek had demonstrated unannounced knowledge of the rubies during his initial police interview, despite no public mention of the jewels having been released.

• Chapter 17: An Aristocratic Gentleman

  • The following morning, M. Carrège interrogated the Comte de la Roche in the presence of Poirot and M. Caux. The Comte maintained an elegant composure, asserting that he had arrived in Nice on the morning of 14 February and had spent that evening gambling at the Casino in Monte Carlo. Ada Mason was brought in but could only state that the Comte resembled the man at the station from behind, unable to make a positive identification. Derek Kettering was subsequently questioned, reiterating that he had not seen his wife on the train, but his slip regarding the rubies heightened official suspicion against him.

• Chapter 18: Derek Lunches

  • Derek drank cocktails at the Negresco Hotel, where Mirelle approached him wearing an orange and black outfit. When Mirelle implied that they could now enjoy the two million pounds together, Derek repulsed her, stating that he was finished with her. Mirelle attempted to charm him back, but Derek walked away and invited Katherine Grey to lunch instead.

• Chapter 19: An Unexpected Visitor

  • At Villa Marina, the Comte de la Roche instructed his servant Hipolyte to tell anyone who asked that he had arrived on Tuesday 14 February, rather than Wednesday 15 February. Mirelle arrived unexpectedly, furiously claiming that Derek Kettering had murdered his wife and urged the Comte to denounce Derek to the police. After Mirelle left, the Comte retrieved a small parcel from a secret drawer in his desk, set a hair trap to detect intruders, and drove to Mentone, mailing the package at a post office while evading police tailing cars. Upon returning, he discovered that his room had been searched and the hair displaced, confirming police scrutiny.

• Chapter 20: Katherine Makes A Friend

  • Katherine and Lenox spent time together at Villa Marguerite, developing a close acquaintance. Poirot phoned Katherine to request an interview on behalf of Van Aldin, and drove her to Nice. Van Aldin thanked Katherine sincerely for offering comfort to Ruth during her final hours. Knighton was noticeably captivated by Katherine, and Poirot noted the growing connection between them.

• Chapter 21: At The Tennis

  • Knighton drove Katherine to a tennis tournament in Cannes, where Poirot joined them. Derek Kettering appeared, acting tense and irritable. Poirot produced a blue leather cigarette case marked with a gold "K" found in Ruth's carriage, but Derek denied owning it. Poirot drew Van Aldin's attention to M. Papopolous, an antique dealer suspected of receiving stolen gems. Poirot then privately displayed to Van Aldin the parcel he had intercepted from the post office containing the Heart Of Fire rubies, revealing that the gems were actually clever imitations.

• Chapter 22: M. Papopolous Breakfasts

  • Poirot visited M. Papopolous and his daughter Zia at their hotel during breakfast, showing them the counterfeit rubies. Papopolous confirmed they were high-grade imitations. Poirot reminded Papopolous of a favour he had performed for him 17 years earlier in Paris regarding a missing item, prompting Papopolous to provide a hint about a horse named "The Marquis" running at Longchamp. Zia added that the Marquis was a master criminal who operated in disguise while wearing a white wig.

• Chapter 23: A New Theory

  • Poirot met Van Aldin and re-examined Ada Mason regarding the blue leather cigarette case. Mason admitted that Ruth had bought the case as a gift for her husband. Poirot pointed out that Derek Kettering shared the exact same physical build as the Comte de la Roche, suggesting that Derek could have been the man seen by Mason at the Gare de Lyon.

• Chapter 24: Poirot Gives Advice

  • Poirot explained to Van Aldin that the Comte de la Roche had only intended to swap the real rubies for imitations, and that an unknown second killer had intervened. Leaving the hotel, Poirot encountered Derek Kettering talking to Katherine Grey and advised him to break off old relationships before pursuing new ones, pointing to Mirelle waiting nearby. Later, Van Aldin called Poirot to report that Ada Mason had changed her story, claiming she was now nearly certain the man at the station had been Derek.

• Chapter 25: Defiance

  • The Comte de la Roche visited Derek Kettering's hotel room and attempted to blackmail him for 100,000 francs, claiming to possess evidence of Derek's guilt provided by Mirelle. Derek rejected the attempt and expelled the Comte. Derek then confronted Mirelle at her hotel, where she admitted telling the Comte a story, but insisted she had personally seen Derek emerging from Ruth's carriage before the train reached Lyons when Ruth was already dead.

• Chapter 26: A Warning

  • In the Casino gardens at Monte Carlo, Poirot cautioned Katherine Grey that while a woman might forgive a thief, she could never love a murderer, subtly warning her against Derek. Derek joined Katherine shortly after, declaring his love for her and swearing that he had not killed his wife, though admitting he had opened Ruth's compartment door, seen her lying still, and left without speaking to her. Knighton arrived and interrupted them, prompting Derek to leave. Knighton then stammeringly declared his own feelings for Katherine. Left alone, Katherine experienced a vivid sensation that Ruth Kettering's spirit was beside her, urgently trying to communicate a secret.

• Chapter 27: Interview With Mirelle

  • Knighton informed Poirot that Mirelle was demanding to see Van Aldin. Poirot and Knighton visited Mirelle, who flew into a rage and declared that Derek had boasted of his plan to murder Ruth. They escorted Mirelle to M. Carrège, where she signed an official statement accusing Derek. Poirot questioned her about the rubies, noting her nervous denial. Later, Poirot received a telegram from Inspector Japp at Scotland Yard containing details on "The Marquis", a gentleman thief who used underlings to commit crimes.

• Chapter 28: Poirot Plays The Squirrel

  • Poirot visited Lenox Tamplin, who suggested that an intruder could have boarded the train at Lyons, committed the crime, stolen the rubies, and stepped off, meaning Ruth was alive when Derek visited her. Poirot later dined with Papopolous and Zia, and observed Mirelle arguing with Papopolous at the Casino regarding money. Strolling in the gardens with Zia, Poirot recalled how he had shielded her 17 years earlier when she was 16 after she had been duped by an assistant named Antonio Pirezzio. In gratitude, Zia revealed that the real rubies had been delivered to her father in Nice by a woman.

• Chapter 29: A Letter From Home

  • Katherine received a letter from Miss Viner in St. Mary Mead, who revealed she was terminally ill and offered Katherine a home if her new fortune failed her. Katherine joined Lenox and Poirot for lunch in Nice alongside Van Aldin and Knighton. Van Aldin mentioned returning to London in two days. Poirot then travelled to Villa Marina in Antibes, where he broke the alibi of the Comte's servants, forcing Hipolyte and Marie to admit that the Comte had actually arrived on Wednesday 15 January, not Tuesday. Poirot subsequently confronted Mirelle, accusing her of entering Ruth's compartment after Lyons and finding her dead, causing Mirelle to collapse in hysterics.

• Chapter 30: Miss Viner Gives Judgment

  • Katherine returned to St. Mary Mead to assist Miss Viner and received a letter from Poirot in Paris hinting at their ongoing partnership. Major Knighton motored down from London to visit Katherine, enjoying a lunch of steak and cheese. Miss Viner observed Knighton's devotion toward Katherine and pronounced his feelings genuine.

• Chapter 31: Mr. Aarons Lunches

  • In London, Poirot lunched with theatrical agent Joseph Aarons, who shared details about Kitty Kidd, a talented male impersonator and character actress who had abandoned the stage three years earlier to go to France with a nobleman known as a Marquis. Aarons added that Mirelle was currently boasting of wearing a massive ruby on a chain, which she called Heart Of Fire.

• Chapter 32: Katherine And Poirot Compare Notes

  • Poirot and Katherine met for lunch at the Savoy in London. Poirot revealed that he had visited the Russian Embassy in Paris, using the threat of press exposure to learn that the stolen jewels had been transferred outside by a man wearing a white wig who walked with a springy step. Poirot added that he had interviewed a theatrical agent and a Harley Street doctor. Katherine presented Poirot with a newspaper clipping regarding a jewel robbery at Lady Tamplin's hospital during the war.

• Chapter 33: A New Theory

  • Poirot conferred with Van Aldin and Knighton, presenting a new theory that Derek Kettering was innocent and that the true killer remained at large. Poirot convinced Van Aldin and Knighton to accompany him back to France on the Blue Train to retrace the crime on site.

• Chapter 34: The Blue Train Again

  • On board the Blue Train, Poirot, Van Aldin, and Knighton re-enacted the movements of the night of the murder. As the train approached Lyons, Poirot stated that no man had exited the train at Lyons, but that a woman disguised as a young man in an overcoat had. Poirot identified this woman as Kitty Kidd, alias Ada Mason. Turning to Knighton, Poirot presented him with his missing blue leather cigarette case, revealing that Knighton himself was the master criminal known as M. le Marquis. French police officers waiting in the corridor stepped forward and arrested Knighton.

• Chapter 35: Explanations

  • At the Negresco in Nice, Poirot explained the entire plot to Van Aldin. The disfigurement of Ruth's face had been designed to obscure the exact time of death and identity details. Knighton and Ada Mason were accomplices who had both entered Van Aldin’s and Ruth's employment two months prior. Knighton had murdered Ruth on the train prior to reaching the Gare de Lyon. Ada Mason, a skilled character actress, had dressed in Ruth's fur coat and red hat at the station, purchased the dinner basket, and informed the conductor that her maid had been left behind in Paris. At Lyons, Mason had changed into male attire, left the train, and returned to Paris to establish an alibi at the Ritz. Knighton, who had faked his War limp, had planted the duplicate rubies on the Comte de la Roche and attempted to frame Derek Kettering. Katherine Grey had intuitively deduced Knighton's involvement through her spiritual impression of Ruth.

• Chapter 36: By The Sea

  • At Villa Marguerite, Poirot sat on the terrace with Lenox Tamplin overlooking the sea. Poirot informed Lenox that Derek Kettering had been cleared of all charges and had travelled to St. Mary Mead to see Katherine Grey. Lenox acknowledged that Derek needed Katherine's steadying influence. As the distant whistle of the Blue Train sounded, Poirot comforted Lenox with the proverb that journeys end in lovers meeting, advising her to trust in the journey of life and in Hercule Poirot.