The Murder of Roger Ackroyd critiques a class system in which money and status allows people to get away with murder, and the class divides means that secrets must be kept.

We find out in the novel that Mrs. Ferrars, a wealthy young widow, commits suicide after killing her husband through slowly poisoning him. Had she been a poorer person, she would have been tried for the murder of her husband and convicted, but because she is rich, she is able to pay blackmail money to keep her crime quiet. Dr. Sheppard knows what really happened but would rather collect her hush money than expose what he knows so that justice can be served. He is also willing to murder Ackroyd when he fears his blackmailing will become public knowledge. Sheppard's status as a doctor and a member of the upper classes helps shield him from being suspected as a criminal.

When Roger Ackroyd is murdered, the initial response of the upper-class characters is to suspect someone from the lower classes. The lower classes are not responsible for the murder, but Poirot's investigations expose a marriage that has been kept secret because it crossed class lines: the servant, Ursula Bourne, has married the upper-class Ralph Paton. Bourne, too, is more easily suspected of murder based on her perceived lower-class status.

Christie, as she often does in her mysteries, critiques a world in which money and status matter more than justice or open and honest human relationships.