A former Army officer and close friend of Poirot who chronicles their cases, often showing his lack of sophistication compared to Poirot. He serves as a bridge for the reader to understand Poirot's methods.

A shy, awkward door-to-door stocking salesman, whose initials match those of the killer. His activities initially arouse suspicion due to their alignment with the murders.

The first victim, an elderly woman who owned a tobacco shop. She is the aunt of Mary Drower and is remembered as kind despite her challenging circumstances.

The second victim, a young waitress known for her flirtatious nature and love of entertainment. Her relationship with a suspect complicates the investigation.

Betty's sister, characterized by her intelligence and strong-willed nature. Unlike her sister, she shows a deep understanding of the investigation process.

Betty Barnard's romantic partner, known for his dreams reflecting his inner turmoil. His emotional struggles concerning Betty's death make him an early suspect.

The third victim, a respected doctor and art collector. He is wealthy and deeply concerned about his dying wife at the time of his murder.

Carmichael's wife, who is dying of cancer and remains attentive to family dynamics. Her observations offer early clues to the investigation.

Carmichael's younger brother, aspiring to a larger role within the investigation. He expresses skepticism towards the police and forms alliances to pursue his interests.

Carmichael Clarke's secretary, noted for her striking appearance and ambitions. Her interactions with other characters raise questions about her motives.

Alice Ascher's niece and a domestic servant, who shows deep attachment to her aunt and participates in the investigation.

A psychiatrist consulting on the case, who is respectful towards Poirot and discussions involve both psychological and investigative aspects.

Poirot's longtime friend from the police force, known for his teasing nature and supportive role in bringing Poirot cases.

A young, ambitious Scotland Yard inspector handling the murders, often displaying a dismissive attitude towards Poirot's input.