Roger Ackroyd, rich, miserly, the lord of the manor-type, found stabbed to death in his study with a knife in his neck.
Mrs Ackroyd, the widowed sister of RA, comes to live with him with her daughter Flora, but complains they are always kept short of money by the stingy RA
Flora, the daughter of the above, niece of RA, agrees to RA's wish for her to marry Ralph Paton just to get away and gain some independence.
Ralph Paton, not RA's own son, but brought up as if he were. Married secretly to Ursula Bourne, but agrees to marry Flora to get some dosh.
Ursula Bourne, housekeeper/parlourmaid, from a genteel but impoverished Irish family, tells RA that she and Ralph are already married. There is a big quarrel and Ralph goes AWOL.
Major Blunt, a big game hunter, an old friend of RA, who visits once a year, he is secretly in love with Flora
Geoffrey Raymond, secretary to RA, tells Poirot that a salesman of a Dictaphone machine had recently visited RA
John Parker, the butler at Fernly (RA's home), who blackmailed former employer
Elizabeth Russell, housekeeper, mother of Charles Kent (but keeps it a secret)
Charles Kent, a drug addict, who comes to get money from his mother (they meet in the summer house)
Inspector Raglan investigating the case, but it is solved by . . .
Hercule Poirot, who has recently retired and come to live in The Larches where he plans to grow marrows, next door to . . .
Dr Sheppard and his older sister Caroline, both of whom are unmarried. The doctor is the narrator of the story, writing it up. In the twist at the end, we learn that he is also the baddy! It was him who was blackmailing
Mrs Ferrars (he knew she had poisoned her husband), and him who killed RA when the latter discovered he was the blackmailer.
Notes: All the action takes place in RA's study, his living room, his summer house or Dr Sheppard's house. The nearest big town is Cranchester.