The following version of this book was used to create the guide: de Gramont, Nina. The Christie Affair. St. Martin's Publishing Group, 2022.

Nina de Gramont's novel The Christie Affair is written from the main character Nan O'Dea's first person point of view. The novel toys with conventional notions of point of view, plot, and structure. The narrative vacillates between various periods in time and uses the past and present tenses. The following summary assumes a linear structure and relies upon the present tense.

As a girl, Nan O'Dea grows up in England with her mother, father, and three sisters, Megs, Louisa, and Colleen. One summer, Nan's parents allow her to visit her uncle Jack and aunt Rosie in Ballycotton, Ireland, where they run the family farm. Throughout the summer months, Nan falls in love with the Irish countryside. Meanwhile, she is simultaneously falling in love with a jovial local boy named Finbarr Mahoney.

The following summer, Nan returns to Ballycotton, where she and Finbarr renew their close friendship. By the end of the summer, the Great War has broken out. Before Finbarr leaves for the front, he gives Nan a claddagh ring and promises to start a life with her when he returns.

Not long later, Nan leaves Ireland when she learns of her sister Colleen's death. Back in England, Megs tells Nan that Colleen killed herself after getting pregnant out of wedlock with a man who disappeared. Although rattled by her sister's death, Nan fails to see Colleen's story as a warning. Indeed, on the day she and Finbarr are reunited, they have sex before they are married. Finbarr returns to his regiment and Nan discovers she is pregnant.

Nan flees to Ballycotton to seek help from Finbarr and his parents. His parents refuse to let her be with Finbarr and deposit her at the Sunday's Corner Convent in County Cork, Ireland. The convent is designed to punish young women who have gotten pregnant out of wedlock. Only four months after her daughter Genevieve is born, the nuns give the baby up for adoption without Nan's consent. Filled with rage and despair, Nan flees the convent. She informs Finbarr that their daughter has been lost and that she can no longer be with him.

Nan spends the next seven years searching for Genevieve. She soon discovers that Genevieve, renamed Teddy, is living with Archie and Agatha Christie. She devises a plan to seduce Archie, take him away from his wife, marry him, and become Teddy's stepmother.

When Archie tells Agatha he wants a divorce, Agatha disappears, inciting a nationwide police search and investigation. Meanwhile, Agatha is hiding out in Harrogate with Nan, Finbarr, and her new romantic interest, Inspector Frank Chilton. Throughout their time in Harrogate, the new companions squat in a local house they later name the Timeless Manor.

Chilton soon discovers that the deaths of a husband and wife at the local Bellefort Hotel were not an accident. By piecing together a series of clues, he realizes that the murdered husband and wife were in fact a former priest and nun who worked at Sunday's Corner. Nan played a role in their deaths. Agatha urges Chilton not to arrest Nan, and to see her crime as justice.

Nan eventually marries Archie according to her plan. Finbarr eventually returns to Ireland, where he creates a new life with a new woman. Agatha runs off with Chilton, with whom she establishes her own happy life.