Written in 2023 by American author Frieda McFadden, The Coworker is a psychological thriller that charts the mysterious disappearance of Dawn Schiff, an accountant for a nutritional supplement company. Dawn’s coworker, Natalie Farrell, reports her colleague missing and claims concern for her welfare. However, as the investigation evolves to become a murder case, Natalie’s innocence comes under scrutiny. The novel highlights the ways in which the dark side of human nature can manifest in even the most mundane of settings, deliberately blurring the boundaries between victims and perpetrators as it explores the treacherous dynamics of office politics.

Frieda McFadden is a prolific author known for writing dark thrillers set in everyday locations. She is also a practicing physician who specializes in brain injuries. Her bestsellers—including the popular trilogy of The Housemaid, The Housemaid's Secret, and The Housemaid is Watching—have topped the charts of Amazon, the New York Times, Publisher’s Weekly, USA Today, and the Wall Street Journal.

This guide refers to the 2023 Hollywood Upstairs Press e-book edition.

Content Warning: The source material and this guide contain descriptions of self-harm, suicidal ideation, and death by suicide.

Plot Summary

The narrative combines the present-day story of Natalie Farrell with past emails written by her coworker, Dawn Schiff. Natalie’s story is told through her first-person perspective, while Dawn’s emails are primarily addressed to her friend, Mia Hodge. Natalie is a salesperson at Vixed, a nutritional supplement company. Following an affair with her married boss, Seth Hoffman, she is now dating a new employee named Caleb McCullough. Arriving at work one day, Natalie is surprised to see the empty cubicle of accountant Dawn Schiff. Dawn has several quirks, including rigid punctuality and an obsession with turtles, and her coworkers view her as odd. In her own cubicle, Natalie finds a turtle figurine stained with a red substance. Upon answering the ringing phone, she hears a voice that sounds like Dawn say “Help me.”

After a sales visit, Natalie checks on Dawn’s house. The door is unlocked, there are signs of a struggle, and the living room carpet is drenched in blood. The police arrive but do not find Dawn’s body. Natalie lies to the leading investigator, Detective Santoro, about her alibi for the previous evening. Instead of admitting that Caleb left at 9:30 pm, she claims that he stayed the night. Caleb reluctantly agrees to corroborate her story.

Soon, Natalie receives a series of silent calls from a withheld number. Detective Santoro interviews her again because he has discovered an urgent email from Dawn in which she requests a meeting with Natalie. Natalie claims that she never found out what Dawn wanted. On impulse, Natalie asks Seth over for the night. She describes the invitation as a “one-off” because she already ended their affair in response to threats from Seth’s wife, Melinda.

Meanwhile, Dawn’s body is found in a woodland area, beaten beyond recognition. Employees at Vixed tell Detective Santoro that Natalie used to bully Dawn. Although Natalie throws the turtle figurine away, it mysteriously reappears on her desk. Later, while sorting through her laundry basket, Natalie finds a giant blood-covered ceramic turtle. Realizing that the turtle must be the murder weapon, she smashes it and disposes of the pieces. Back at work, Seth suspends Natalie after learning that Dawn found accounting discrepancies relating to Natalie’s sales. Meanwhile, Caleb tells Natalie that he has admitted to providing her with a false alibi. As a result, police officers search Natalie’s home and car.

Natalie has organized a 5K charity run. She claims that the event is in remembrance of her childhood friend, Amelia, who had cerebral palsy. On the day of the run, Natalie receives another silent withheld call. Using an app, she discovers that the call came from a Rhode Island motel. Just as Natalie is being interviewed for TV, Detective Santoro arrests her.

The narrative shifts to a series of emails that Dawn wrote to her friend Mia about her new job at Vixed. Early emails describe her unsuccessful attempts to befriend a glamorous coworker named Natalie. Dawn’s emails also describe Natalie’s increasingly cruel behavior, which includes misinforming Dawn about meeting times, vandalizing her desk, and throwing away the turtle cupcakes that she baked. Shortly before Dawn’s disappearance, she tells Mia that she confronted Natalie about funds that were missing from the company’s accounts. Natalie suggested that they should work together to determine who had taken the money. In her final email to Mia, Dawn explains that she expects Natalie to arrive at 10:00 pm that evening.

At the start of Part 2, Dawn is revealed to be alive and staying in a motel. She avidly watches Natalie’s arrest on the news. Caleb arrives, announcing that he and Dawn must leave the motel because Natalie has traced their call. Caleb is revealed to Dawn’s lover and her accomplice. The narrative explains that Dawn wrote strategic emails to make it appear as though Natalie had a genuine motive to kill her. She also made her home look like a murder scene by cutting herself before her disappearance. Caleb replied to the emails, posing as Mia, and was also the one to plant incriminating evidence in Natalie’s home and car. He also taunted Natalie by placing the turtle figurine on her work desk. Dawn and Caleb are taking revenge on Natalie for the death of Mia (whose full name is Amelia Hodge). Mia had cerebral palsy and was Dawn’s best friend and Caleb’s half sister. She died by suicide after Natalie and her friend Tara Wilkes bullied her in high school.

Now in prison, Natalie learns from her lawyer that Dawn’s blood and hair were found in the trunk of her car. Furthermore, Caleb told police that Natalie asked him to leave at 9:30 pm on the night that Dawn disappeared. The lawyer advises Natalie that she will likely face life imprisonment unless she confesses and accepts a plea bargain. Meanwhile, Dawn and Caleb move to another motel. Due to the results of DNA testing, the police now know that the dead woman in the woods was not Dawn. Dawn worries that Natalie will not be convicted without a body. She also fears that Caleb became attracted to Natalie during their fake romance.

Seth pays Natalie’s bail, declaring that he was wrong to believe she was stealing from Vixed. He also reveals that Caleb knew Dawn before he started working at the company. Natalie and Seth drive to the Rhode Island motel, where the receptionist confirms that Caleb recently checked out with a woman. Later, Caleb finds Natalie and Seth and admits to his part in recent events. He explains that Dawn is not dead but missing, and he needs their help to find her. Caleb fears that Dawn intends to kill herself in order to produce an incriminating dead body. Guessing that Dawn may be planning to drown herself, they check the nearest beaches. Natalie soon finds Dawn on a pier with a cinderblock tied to her ankle.

Furious that her plan has been thwarted, Dawn tries to kill Natalie with the cinderblock. However, Natalie defends herself by spraying Dawn’s eyes with mace. Natalie claims to regret what she did to Amelia. She also emphasizes how much Caleb loves Dawn, describing how he cried when he feared that she would kill herself. Shortly afterward, Natalie learns that the dead woman from the woods has been identified as Tara Wilkes—her high school friend. She realizes that Dawn beat Tara to death.

Dawn explains her disappearance to the police, claiming that she was confused and disoriented for days after a heavy ceramic turtle fell on her head.

A year later, Natalie and Dawn organize the 5K event together in Mia’s memory. The two women appear to be on good terms as they smile and wave at each other. At the end of the run, Caleb proposes to Dawn, and she accepts. Dawn reflects that Natalie has kept quiet about Tara’s murder, which Caleb knows nothing about.

Watching Dawn and Caleb, Natalie muses on her own secrets. As usual, she has skimmed a portion of the fun run proceeds for herself. The previous year, she was forced to transfer the money to cover up funds that she had stolen from Vixed. Natalie is sure that Seth will marry her now that he is officially divorced. In the past, she tried to end his marriage by anonymously tipping off Seth’s wife about their affair. She also pretended that Melinda was threatening her until Seth’s wife started stalking her in reality. Natalie reveals that Dawn knows all about the money she embezzled from Vixed. Nevertheless, she feels confident that her secret is safe, for they are both “dangerous” women.