The following version of this book was used to create the guide: Benedict, Marie. The Mystery of Mrs Christie. Sourcebooks Landmark, 2021.

The Mystery of Mrs Christie tells two stories simultaneously. The first would be the story of how Archie and Agatha met and how they gradually fell out of love with one another. The second plotline sheds light on Archie’s day-to-day life during the eleven days of Agatha’s disappearance.

To begin, Archie and Agatha meet at a dance one night. Archie is struck by Agatha’s beauty and asks her to dance. The two begin a steady courtship, with Archie regularly visiting her home, where she lives with her mother and her sister, Madge. Archie proposes before leaving to be pilot in World War One. While Archie is gone, Agatha works in a hospital and later a pharmacy. She also writes her first mystery novel, The Mysterious Affair at Styles. Agatha and Archie see each other whenever he gets leave. They get married out of the blue one day and start their life together in London.

Agatha does her best to keep Archie happy, but he becomes hard to please after the war. She even prioritizes him over their daughter, Rosalind. Agatha publishes several mystery novels, generating a modest success. Realizing that their marriage is crumbling, she suggests they move to be near one of Archie’s favorite golf courses. They call the new house Styles, after the house in her first novel.

Contrary to Agatha’s expectations, their relationship gets even worse. Archie starts having an affair with a woman named Nancy Neele. He demands that Agatha grant him a divorce. She agrees to do so, under the condition that Archie publicly announces that he is having an affair. He refuses and hits her. The next day, Agatha disappears.

Agatha writes Archie a letter with specific instructions. He must read a manuscript that tells the story of their marriage. He must play the part of loving husband in the police investigations. Archie obeys, irritated all the while by the press’ nagging questions and the policemen who suspect that he murdered his wife. Even the staff are suspicious of him, especially Charlotte who is Agatha’s secretary and Rosalind’s governess. She tells the police about the awful fight Archie and Agatha had the night before her disappearance. News spreads of Archie’s affair, implicating him further in the investigation.

At the end of the novel, Archie meets with Agatha at a hotel where she has been pretending to be Nancy, Archie’s mistress. Agatha explains that she orchestrated her disappearance in the hopes of shedding light on Archie’s infidelity. That way, she would not be held responsible for their divorce and her daughter could never blame her for the two of them breaking up. Archie must publicly confirm the rumors regarding Nancy, or else Agatha will publish the manuscript and make it seem as though Archie tried to kill her. Archie consents to the plan, and Agatha agrees to pretend that her disappearance was the result of amnesia.