Mackenzie digs through her old school papers to find a letter written by the woman who raised her, excusing her from a week of school. She compares the handwriting to the manuscripts and letters she has and realizes that they do not match. She also realizes that she never saw the woman who raised her write. Evelyn offers Mackenzie a trust fund in exchange for signing a non-disclosure agreement.

EJ begs Mackenzie not to go to the E. V. Renge memorial at her university, explaining that she might be in danger. Mackenzie threatens to make a scene, but EJ warns that her grandmother may be dangerous. Like the funeral, the university tribute is a carefully constructed affair. Mackenzie is disgusted by her father’s speech and considers him a liar. She is approached by Professor Robertson, who expresses genuine respect for her mother.

As Mackenzie is talking to Professor Robertson, her grandmother approaches her and attempts to network with him. When she introduces him to Ben, Ben grows pale and walks away in a panic. Robertson also leaves. Mackenzie follows him out and asks how he knows her father, but Robertson insists that he doesn’t. Mackenzie notices that he has a star-shaped scar that matches her mother’s friend John’s.

EJ confirms that Professor John Robertson attended college in Old Bow, Nebraska, the same place where Elizabeth once lived. At Mackenzie’s insistence, he finds John’s address online, and she drives to speak to him. She is relieved to see that he is home, and when he answers the door, she demands to know everything that he knows about her mother.

John confirms that he was once close to Elizabeth but explains that he never spoke to her again after she left Old Bow. He claims that Ben never deserved Elizabeth and that he only used her for sex and, after he realized her talent, for the prestige of dating a soon-to-be-famous author. John suggests that Ben’s family only accepted her because they knew she would be famous. He is startled when Mackenzie mentions Tonya.

John reads the letters from Elizabeth and seems heartbroken by the contents. He reveals that Elizabeth told him she was going to break up with Ben on the night she confronted him and that he planned to help her with the baby and support her financially. Mackenzie asks him why he never contacted her when she disappeared, and he says that he was too hurt by her disappearance. When Mackenzie shows him a picture of young Elizabeth, he confirms that she is Tonya.

John explains that after assigning Lies, Lies, and Revenge to Mackenzie’s class, he read the book and recognized it as Elizabeth’s first novel. When he tried to find her, he realized that the woman calling herself Elizabeth was Tonya. John warns that Mackenzie is unlikely to have success finding her biological mother without the police. John agrees to accompany Mackenzie back to Old Bow to investigate the disappearance.

Mackenzie is approached by Detective Jimenez, who shows her a photo of the mystery man who was kicked out of her mother’s funeral and later met with her grandmother and father at their home. Mackenzie tells Jimenez that the man was at her home recently and drops hints about her theories that Tonya has replaced Elizabeth. Mackenzie hopes that she is giving enough detail for the detective to investigate on his own.

Mackenzie is summoned to her grandmother’s house, where she signs non-disclosure agreements regarding her mother’s literary estate in exchange for money from her mother’s trust. She attempts to search her mother’s room for more evidence of the switch but finds that all personal items have been removed. EJ suggests that Ben and Evelyn are trying to hide evidence.

When Mackenzie calls Dianne with updates about her theories, Dianne offers to join her and John in Old Bow to investigate the real Elizabeth’s disappearance. EJ offers to come with them, but Mackenzie tells him to stay. EJ asks Mackenzie to go to dinner with him when she returns. When Mackenzie jokingly accepts, EJ assures her that it will be a real date and that he is interested in her romantically.

In Old Bow, Dianne, John, and Mackenzie meet with a college professor, who complains that Elizabeth never agreed to come back and visit the college. They visit Elizabeth’s old apartment and learn that the old superintendent has been in prison after being arrested for dealing drugs. Mackenzie notices a sign about sharp-toothed garfish and remembers that her mother’s unfinished novel was called Sharp Teeth. She leaves with no clues.

On the drive out of town, Mackenzie notices a storefront for Huckleberry Supplies, the company that called her parents’ home about an overdue bill. A worker reveals that the overdue account is owned by an LLC and that the account has been active for 20 years. When Dianne threatens the worker with police interference, she agrees to give the group the local address for the account.

Mackenzie, John, and Dianne drive to the address, a lakeside cabin. A woman stops them. She claims that she is a caretaker for the resident, a mentally fragile woman who spends her days writing. As the caretaker insists that the group leave, the woman appears. She immediately goes to Mackenzie, who instantly recognizes her as her mother. The women share an emotional reunion.

Mackenzie, EJ, Dianne, John, and Elizabeth celebrate Thanksgiving dinner together. Although Elizabeth is still mentally fragile and nonverbal, Mackenzie senses that she is happy. Ben and Evelyn have been arrested for fraud and identity theft, with all their stolen money transferred to a trust that Mackenzie runs. Elizabeth’s books are being republished under her real name, and Mackenzie has been approached to write a book about her mother’s experience.

After Thanksgiving dinner, Mackenzie receives a final letter from her mother’s diary implying that Ben is not her biological father. While crying in John’s bathroom, she sees a prescription that she also takes and realizes that they share the same hereditary disease. She realizes that John is her biological father. John confirms that he realized it was likely as soon as he learned that she was Elizabeth’s daughter. Mackenzie feels as if she finally has a family.

Dianne and EJ sit alone while Mackenzie, John, and Elizabeth reunite as a family. Dianne hopes that they stop investigating the situation and privately remembers how she caused Tonya’s death. After seeing Tonya posing as Elizabeth on a dust jacket, Dianne began stalking her. She followed Tonya to a hiking trail and threatened to expose her. While mocking Dianne, Tonya slipped and hit her head, dying instantly.

The narrative reveals that Wallace King, also known as Grunger, the superintendent of Elizabeth’s college apartment, realized that Tonya was posing as Elizabeth and blackmailed her into supporting him after prison. He was the mystery man at Elizabeth’s funeral who argued with Ben and Evelyn. He has also been sending Mackenzie pages from Elizabeth’s diary, which he stole from her apartment the night before he was arrested. Grunger’s goal was to take revenge on Tonya for choosing Ben over him.