The Other Mrs. by New York Times—bestselling author Mary Kubica tells the story of Sadie Foust and her family, who have relocated from urban Chicago to rural Maine, only to be shocked by the violent murder of a neighbor. To save herself and her children, Sadie must solve the mystery and assemble the disturbing pieces of the past and present into a coherent whole. The family’s story is revealed through a fragmented narrative of shifting points of view, narrative voices, and time periods.

Mary Kubica’s suspenseful novels have won critical acclaim and a wide readership. Online literary magazine Indiebound named her debut, 2014’s The Good Girl, an Indie Next Pick, and her work has received rave reviews in Kirkus, Chicago Tribune, and the Los Angeles Times.

This guide refers to the ebook version of the novel, published by Park Row in 2020.

Content Warning: The novel contains graphic descriptions of suicide and references to animal and child abuse, and centers on the mental-health condition of dissociative identity disorder (DID).

Plot Summary

The early part of the story is told by a first-person narrator, Dr. Sadie Foust. Sadie and her family arrive in Maine after her husband’s sister, Alice, dies by suicide. Will inherits her house and guardianship of his troubled teenage niece, Imogen. Sadie is hesitant about the move, finding Will’s desire for a “fresh start” somewhat elusive, but too many bad things have happened recently in Chicago (including Will having an affair), so this move could be fortuitous for the entire family.

The family’s “fresh start” is soon interrupted when their neighbor, Morgan Baines, is stabbed to death. The word DIE is also carved into the ice on Sadie’s car window, leading to concerns that one of the teenagers in the house is acting out. Each child is dealing with trauma: Imogen found her mother’s body, and Sadie’s oldest son, Otto, brought a knife to his former school to ward off bullies. A new first-person narrator, Camille, is introduced. She is someone from Sadie’s and Will’s past, and she tells about their history in a series of flashbacks.

Sadie finds a picture of Will’s long-deceased fiancée and wonders how she can be jealous of a woman who has been dead for 20 years. Clues about Morgan’s murder, such as threatening notes she received, are revealed by an investigating police officer. Sadie uses these clues to try to solve Morgan’s murder. She also learns that her neighbors, the Nilssons, reported seeing her in a physical altercation with Morgan shortly before the murder; she knows this cannot be true because she never met Morgan before.

Another narrator, Mouse, is introduced, and her sections are told in the third person. The author leads readers down one of many false trails by making Mouse the same age as Morgan’s and Jeffrey’s unnamed six-year-old daughter. Jeffrey is Morgan’s husband and, in Sadie’s mind, the number one murder suspect. At her job at the island’s local clinic, Sadie engages in strange play with a child patient but is unable to remember why she is on the floor.

Sadie continues to build theories about the murder, at times suspecting Imogen, Otto, Jeffrey, and Jeffrey’s ex-wife, Courtney. Her narration alternates with Camille’s, who shares that she and Sadie were roommates and she has slept with Will, and Mouse’s, whose “once upon a time” entries are starting to become ominous. When Sadie discovers a murder scene staged in a dollhouse and violent drawings in the attic, she realizes that the murderer has been in her house. Clues such as the murder weapon (a boning knife) and Morgan’s phone are later found in the house. Sadie is beginning to experience noticeable memory problems and episodes of lost time. Her response is to rationalize or deny them. She also begins to have dreams in which she has out-of-body experiences and auditory hallucinations.

Sadie’s darker side, which appears in previous sections when she snoops in patient files, returns when she breaks into Courtney’s home. Officer Berg still considers Sadie a suspect in Morgan’s murder, and her theory that he is bribing the Nilssons to testify against her is undermined. Sadie discontinues her search of Courtney’s house to attend to Imogen’s truancy problems at school. The teen meets Sadie in a graveyard and reveals that her mother forced her to help with her suicide attempt.

Upon returning home, Sadie discovers a silver necklace with the initial M, a bloody washcloth, and the missing boning knife, all of which she reports to the police and Will. When the police search the house for this evidence, however, it is gone. Also gone is Sadie’s alibi, as Will tells the police that Sadie left the house that night and that she has a very jealous nature. During her interview at the police station, Sadie transitions into Camille, and the psychiatrist who meets with her explains that Sadie has dissociative identity disorder (DID). Camille and Mouse are not separate people but Sadie’s alternate personalities. Will’s affair is not with a stranger but with Camille.

Sadie returns home from the police station, and Will decides he must kill her to protect himself. Will’s entries, told in the first person, introduce the novel’s fourth and final narrative voice. He confesses that his fiancée, Erin, did not die in an accident; he murdered her, and he manipulated Camille into murdering Morgan, Erin’s little sister. He worried Morgan would reveal the truth about Erin’s death being murder rather than suicide. Will tells Sadie he convinced Camille to murder his graduate student, Carrie, who accused him of sexual harassment. Will first tries to poison Sadie, but when she finally realizes the truth about him, he decides to strangle her instead. A violent struggle ensues, and Imogen hits him over the head, allowing Sadie to kill him. An Epilogue finds the family on the path to healing in their new California home with Sadie exonerated of all crimes.