| 1 | Arthur | Hastings | Narrator. |
| | John | Cavendish | Hasting's acquaintance. |
| | Mrs. | Cavendish | John's mother. |
| | Mr. | Cavendish | John's father. |
| | Lawrence | Cavendish | John's brother. |
| | Alfred | Inglethrop | Emily's new husband. |
| | Cynthia | | Mrs. Cavendish's protégé. |
| | Evelyn | Howard | Emily's closest friend. AKA: Evie. |
| | Mary | Cavendish | John's wife. |
| | Emily | Inglethrop | Alfred's mother. The owner of Styles Court. |
| | Mr. | Inglethrop | Alfred's father. |
| | Dr. | Bauerstein | A doctor expert in poisoning. |
| | Cynthia | Murdock | Daughter of Emily's close friend. |
| | Mrs. | Raikes | Emily's neighbor. |
| 2 | Lady | Tadminister | The first lady of Tadminister. |
| | Mrs. | Rolleston | Lady Tadminister's sister. |
| | Hercule | Poirot | Protagonist. |
| | Dorcas | | Parlour maid. |
| 3 | Dr. | Wilkins | Emily's doctor. |
| | Annie | | One of the house maids. |
| 4 | Mr. | Wells | Emily's lawyer. |
| | Ross | | The caterer in Tadminister. |
| | Manning | | Emily's gardener. |
| | William | | The young gardener. |
| | Cook | | Emily's chef. |
| 5 | Mr. | Mace | The chemist shop owner. |
| 6 | James | Japp | Scotland Yard detective inspector. AKA: Jimmy. |
| 7 | Summerhaye | | Japp's superintendent. |
| 11 | Ernest | Heavyweather | John's lawyer. |
| | Mr. | Philips | Prosecution lawyer. |