Agatha is an aspiring writer who meets and marries a young pilot right before World War I. She commits herself entirely to domestic duties and her husband's happiness, following traditional advice that demands she prioritize him above all else. Over time, she develops a successful career writing detective fiction, which causes friction in her household. Her sudden disappearance triggers a nationwide search and intense press scrutiny.

Archie is a former Royal Flying Corps pilot whose experiences in the war leave him prone to dark moods. He insists on being the absolute center of his wife's world and resents anything that diverts her attention, including their child and her writing career. When Agatha goes missing, his primary concern shifts to protecting his own reputation and concealing his infidelities from the police.

Rosalind is the seven-year-old daughter of Agatha and Archie. She struggles with the emotional distance of her parents, particularly her mother, who was advised to put Archie's needs above her child's. She physically resembles her father and possesses a similarly stolid temperament, which occasionally endears her to him.

Kenward is the chief police officer overseeing the investigation into Agatha's disappearance. His untidy appearance masks a sharp, suspicious mind that immediately zeroes in on Archie as a primary suspect. He seems to take satisfaction in unsettling the wealthy individuals involved in the case.

Agatha's mother holds traditional, late-Victorian views on a woman's role in marriage. She consistently advises her daughter to anticipate her husband's every need and keep him entertained. Though she initially questions Archie's lack of financial standing, she eventually champions him as the head of Agatha's household.

Agatha's older sister possesses a more modern outlook on relationships and independence than their mother. A friendly sibling rivalry over writing mysteries originally spurs Agatha to draft her first novel. Madge provides crucial emotional support as Agatha's marriage begins to fracture.

Charlotte is a governess and secretary employed at the Christie household, known as Styles. She cares for Rosalind and manages domestic affairs. She finds herself caught in the middle of a police investigation, forced to weigh her loyalty to her employers against her duty to tell the truth.

Goddard is a meticulously dressed police officer from the Berkshire Constabulary. His neat appearance and polite demeanor make Archie mistakenly believe they share a class kinship. In reality, Goddard uses his agreeable nature to subtly extract information from suspects.

Nancy is a young woman who enters into a romantic relationship with Archie. She represents the quiet, unobtrusive feminine ideal that Archie desires as an alternative to his independent wife. Her relationship with Archie becomes a closely guarded secret during the police investigation.

Reggie is a military man stationed in Hong Kong. He has an informal agreement to marry Agatha, though he permits her to attend social events with other men while he completes his service overseas.

Archie's mother presents a kind face to Agatha but privately disparages her modern tendencies. She becomes highly distressed by the media coverage surrounding her daughter-in-law's sudden disappearance and demands answers from her son.

Archie's brother does not maintain regular correspondence with Agatha. He receives an unexpected letter from her posted from London on the first morning of her disappearance.

Sam is a friend of Archie who hosts a weekend gathering just as the news of Agatha's disappearance breaks. He provides a comfortable, elegant social setting that Archie frequently prefers over his own home.

Madge James is Sam's wife and a friend to Nancy Neele. She helps facilitate the weekend gathering that serves as Archie's alibi when the police arrive at his house.

Agatha's great-aunt adopted Agatha's mother and provides a steady, supportive presence at the family estate, Ashfield. She celebrates Agatha's cleverness and resourcefulness.