Hercule Poirot

Katherine Grey

Poirot respects Katherine's intelligence and integrity, forming a trusting alliance during the investigation.

Ruth Kettering

Poirot investigates Ruth's murder, interacting with her primarily through clues and witness accounts.

Derek Kettering

Derek is initially hostile and suspicious of Poirot's investigation, fearing he will be accused.

Major Knighton

Poirot interviews Knighton as a key witness and assistant in the case, maintaining polite cooperation.

Comte de la Roche

The Comte is a prime suspect and tries to outmaneuver Poirot, leading to tense confrontations.

M. Papopolous

Poirot consults Papopolous, an antique dealer, for information about stolen jewels.

Lenox Tamplin

Poirot finds Lenox a sensible and helpful ally during his stay at the villa.

Zia

Zia, a maid, provides Poirot with key observations about the household.

George

George is Poirot's loyal valet, assisting him with travel and daily needs.

Katherine Grey

Poirot respects Katherine's intelligence and integrity, forming a trusting alliance during the investigation.

Ruth Kettering

Poirot investigates Ruth's murder, interacting with her primarily through clues and witness accounts.

Derek Kettering

Derek is initially hostile and suspicious of Poirot's investigation, fearing he will be accused.

The Mystery of the Blue Train

The famed detective who is called upon to investigate the murder aboard the Blue Train.

X: On the Blue Train

Dines opposite Katherine Grey; discusses detective novels and hints at future adventures.

XI: Murder

Present during the police questioning; examines the compartment and notes the strange post-mortem blow; invites Katherine to join the investigation.

XIV: Ada Mason's Story

Present at the interrogation, offers his services to Van Aldin, and acts as interpreter.

The Comte de la Roche

Questions the Comte's psychology as a murderer and reveals his knowledge of the Comte's whereabouts.

XVI: Poirot Discusses the Case

Poirot leads the discussion, challenges the police's theory, and agrees to work for Van Aldin.

An Aristocratic Gentleman

Observes Kettering's reactions and notes the discrepancy about the rubies; later questions the maid about the tickets.

Katherine Makes a Friend

Calls Katherine to arrange a meeting with Van Aldin, picks her up in an auto, discusses the case and the Comte de la Roche's alibi.

At the Tennis

Arranges to meet everyone at the tennis; produces a cigarette case and later reveals the recovered rubies to Van Aldin.

M. Papopolous Breakfasts

Visits M. Papopolous early in the morning, shows him the imitation rubies, and seeks his help in the murder investigation. Later sends a coded telegram to Inspector Japp.

A New Theory

Presents his new theory to Van Aldin, re-interviews Ada Mason, and reveals the jewels were imitations.

XXIV: Poirot Gives Advice

Explains his theory of the crime to Van Aldin, warns Derek about Mirelle, and receives confirmation from Van Aldin about Mason's identification.

A Warning

Poirot warns Katherine about a man more dangerous than the Comte de la Roche, implying that the man may be a murderer.

Interview with Mirelle

Accompanies Knighton to interview Mirelle, takes the lead in the conversation, and later questions Mirelle's statement during the official interrogation.

XXVIII: Poirot Plays the Squirrel

Plays the squirrel, orchestrating meetings and gathering information; visits Lady Tamplin's villa, dines with Papopolous, and confronts Zia.

A Letter from Home

Visits the Villa Marina to confront Hipolyte and Marie about the Comte's arrival; interrogates Mirelle about entering Ruth's compartment.

Miss Viner Gives Judgment

Poirot writes to Katherine from Paris, updating her on his inquiries and expressing a desire to meet her in London.

XXXI: Mr. Aarons Lunches

Hosts Mr. Aarons at lunch and questions him about Kitty Kidd and Mirelle, showing keen interest in the ruby 'Heart of Fire.'

XXXII: Katherine and Poirot Compare Notes

Dines with Katherine at the Savoy, admits dissatisfaction with the case against Derek Kettering, and reveals his investigations in Paris and London.

A New Theory

Presents a new theory exonerating Derek Kettering and proposes traveling to the south of France.

The Blue Train Again

Orchestrates the reconstruction of the crime on the Blue Train, ultimately exposing Knighton as the murderer.

Explanations

Provides the full explanation of the murder to Van Aldin, detailing his deductive process.

By the Sea

Sits with Lenox on the terrace, recounts the story he told Van Aldin, and offers her comfort and wisdom.