Katherine Grey

Hercule Poirot

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

Derek Kettering

Derek is drawn to Katherine's calm and genuine nature, developing romantic interest after his wife's death.

Ruth Kettering

Katherine meets Ruth on the train and has polite but brief interactions before Ruth's murder.

Lenox Tamplin

Katherine and Lenox become friendly companions during Katherine's stay at the Tamplin villa.

Lady Tamplin

Katherine is a guest of Lady Tamplin, who treats her with superficial hospitality.

Comte de la Roche

The Comte attempts to charm and manipulate Katherine for his own ends.

Major Knighton

Katherine and Knighton share a cordial, supportive relationship as they assist Poirot.

Hercule Poirot

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

Lenox Tamplin

Katherine and Lenox become friendly companions during Katherine's stay at the Tamplin villa.

Hercule Poirot

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

Ruth Kettering

Katherine meets Ruth on the train and has polite but brief interactions before Ruth's murder.

Derek Kettering

Derek is drawn to Katherine's calm and genuine nature, developing romantic interest after his wife's death.

The Mystery of the Blue Train

A fellow passenger who becomes an unwitting witness to the events on the train.

VI: Mirelle

Briefly encountered by Derek in the corridor; he later muses on her as 'Portrait of a lady with grey eyes.'

Letters

Receives letters about her inheritance, reflects on her past as a companion, and decides to travel and buy new clothes.

Lady Tamplin Writes a Letter

Visits lawyers, arranges a sum for Mrs. Harfield's relatives, shops for clothes, and books a trip to the Riviera after receiving Lady Tamplin's letter.

An Offer Refused

Katherine is seen at Thomas Cook & Sons booking a ticket on the Blue Train to Nice, coincidentally on the same day as Derek.

X: On the Blue Train

Travels on the Blue Train; listens to Ruth's confidences and later dines with Hercule Poirot.

XI: Murder

Wakes to sunshine, identifies the murdered woman, and agrees to help Poirot investigate.

At the Villa Marguerite

Katherine is the guest at Villa Marguerite, recounting the murder to Lady Tamplin and her family. She feels uncomfortable with Lady Tamplin's schemes and later remembers seeing a man enter Ruth's compartment, but decides not to tell the police.

XVIII: Derek Lunches

Katherine arrives at the Negresco and is invited by Derek to have lunch with him.

Katherine Makes a Friend

Sits on the terrace with Lenox, discusses Derek Kettering, receives a phone call from Poirot, meets with Van Aldin to recount her conversation with Ruth.

At the Tennis

Attends the tennis match with Knighton and Poirot; is questioned about the cigarette case.

XXIV: Poirot Gives Advice

Arrives in a car outside the hotel; Derek speaks with her earnestly before she drives off.

A Warning

Katherine is the focal point of the chapter, receiving warnings and declarations from both Derek Kettering and Major Knighton, and sensing the presence of Ruth Kettering.

Interview with Mirelle

Mentioned as having confirmed seeing Derek Kettering go into his wife's compartment before the train reached Lyons.

A Letter from Home

Reads a letter from Miss Viner and feels a longing for home; later lunches with Poirot and Lenox.

Miss Viner Gives Judgment

Katherine is staying with Miss Viner, reading letters from Poirot and Knighton, and arranging Knighton's visit.

XXXII: Katherine and Poirot Compare Notes

Meets Poirot at the Savoy, shares a newspaper cutting, and expresses emotional urgency for the case to be resolved.

Explanations

Mentioned as having sensed Ruth's presence and acted on her intuition about Knighton's guilt.

By the Sea

Mentioned as reserved and untrusting; Lenox had wrongly thought she cared for Knighton.