At her mother’s funeral, Mackenzie Casper struggles with complex feelings. She feels as if her mother never truly cared about her and resents the spectacle that her mother’s editors have made of her funeral. She sees her father argue with a strange man who calls him “Benny-Boy” and mentions her name. He claims not to know the man. After sneaking out, she finds a mysterious letter in her car signed by her mother’s number-one fan.

Mackenzie looks around the vacant parking lot for a clue as to who left the letter. Via phone, Mackenzie’s best friend, EJ, encourages her to open the letter. Mackenzie is reluctant, knowing that fans have sent her mother strange things in the past. Inside the envelope, she finds three handwritten pages. The first page asks if she wants to know a secret and is signed by her mother.

Mackenzie drives to her parents’ home and sneaks into her mother’s always-locked office using a secret key that her father made. She believes that the fact that her father had a secret key reflects the rough state of their relationship. Once inside, Mackenzie uses one of her mother’s manuscript pages to determine that the letter she received is, in fact, from her mother.

In the letter, Elizabeth describes how she first met Mackenzie’s father, Ben, while at college. From the beginning of their relationship, she knew that rich, popular Ben was only interested in her because she was a talented writer. However, she was so charmed by him that she ignored the warning signs. The letter alludes to sexual abuse in her childhood and urges the reader to ignore gossip about her personal life.

Mackenzie discusses the letter with EJ, who seems intrigued by the details of her parents’ first night together. Mackenzie is more interested in revelations about a strange woman whom the letter implies ruined her mother’s life. Although she is struggling to process her mother’s sudden absence, she is certain that what she is feeling is not grief. She fears that the letter means more bad things are coming.

A drunk couple interrupts Mackenzie and EJ, causing EJ to leave. Mackenzie is annoyed at the crowds of people filling her house for the post-funeral reception. She overhears her grandmother Evelyn and father, Ben, arguing in her mother’s office. Evelyn reveals that the police believe that Elizabeth’s death was not an accident. Ben suggests that Elizabeth’s death was a long time coming.

Mackenzie struggles to focus on her college classes as she scrolls through social media, reading updates about her mother’s fans’ celebrations of her life. She recalls being outed as E. V. Renge’s daughter after a professor named Robertson assigned her class an assignment on the virality of her mother’s work. Since the discovery of this family connection, Mackenzie’s classmates, especially a girl named Sarah, have treated her differently.

Professor Robertson asks Mackenzie how she is handling her mother’s death, and she doesn’t have the heart to tell him that she and her mother were not close. Robertson also questions her about her health. Three weeks earlier, Mackenzie had a seizure in his class; she has now been diagnosed with an unnamed hereditary disorder. Although she revealed her condition to Robertson, she has not told her parents. Later, Mackenzie arrives home to find another letter.

In the letter, Elizabeth reveals that she was assaulted by three boys in the group foster home that she lived in as a teenager. A month later, the boys died in a mysterious barn fire. Elizabeth used her trauma as inspiration in her first novel but devised a more violent and gory ending for the boys. While writing the novel in college, she was confronted by a mysterious woman from her past, Tonya Shaffer, who claimed to know how Elizabeth avenged her assailants.

Mackenzie brings the letter to EJ to examine. When she arrives, she finds his ex-girlfriend, Monica, leaving. Mackenzie feels jealous and then pushes the feelings aside. EJ notes that the story in the letter aligns closely with the events of the first E. V. Renge novel, Lies, Lies, and Revenge. He confirms via online research that a fatal barn fire occurred at the foster home where Elizabeth was raised.

EJ offers to find the police file related to the foster home barn fire so that they can determine if Elizabeth was a suspect. Mackenzie returns to her parents’ house, not wanting her father to be lonely. When she arrives, she finds him drunk in her mother’s office, using a screwdriver to open locked cabinets. She laughs at the thought that her mother was so protective of her secrets.

Ben claims to be looking for insurance papers, explaining that he, Elizabeth, and Mackenzie all have life insurance policies. Mackenzie wonders if her mother knew about her hereditary disease and established a policy because she expected Mackenzie to die. She also suspects that the life insurance paperwork would be with their lawyers and wonders what secret files her father is truly searching for.

Mackenzie asks Ben about her mother’s college years, hoping for more information about John, a friend mentioned in the second letter. Ben says that Elizabeth never had any friends but that she was kind and fun until an unnamed event occurred. As he gets increasingly drunk, Ben also reveals that Elizabeth had an affair behind his back for many years.

Mackenzie makes a copy of her father’s secret spare key to her mother’s office so that she can get in whenever she likes. She learns that her father has ordered their housekeeper, Minna, to throw out all the flowers that admirers sent. Mackenzie asks Minna to keep one large arrangement that was addressed to Elizabeth as the “finest woman” the sender has ever known. Minna gives Mackenzie an envelope with another letter from her mother.

Tonya began spending time with Ben, making Elizabeth jealous and insecure. On a night out with Ben and his friends, Elizabeth was horrified when Tonya recounted the story of the foster home fire, not revealing Elizabeth’s involvement. When Elizabeth tried to leave, Tonya followed her and claimed to have proof that Elizabeth was involved with the fire. Tonya threatened to go to the police with her evidence.

EJ arrives and reads the third letter, confirming that it seems like an admission that Elizabeth was involved in the murder of her three assailants. When he finds Mackenzie’s prescription bottles, he seems worried and tells her that he wants her to stay alive. Mackenzie teases him about his computer-science girlfriends, but he insists that he’s not interested in that type of girl anymore.

Minna’s nephew Nick helps her remove all the flower arrangements from the house. EJ and Mackenzie sneak into Elizabeth’s locked office using the copied key. Mackenzie notices that her father has moved his spare key from its usual hiding spot. All the gothic decorations and paraphernalia amaze EJ, and he and Mackenzie search through decades of fan mail and presents.

EJ finds a locked drawer in a cabinet and suspects that the contents inside are important. While he tries to find a key to unlock it, Mackenzie begins searching through her mother’s desk. Sitting at her mother’s desk makes her feel closer to her mother. She finds her grandmother Evelyn’s name on legal documents and evidence that her mother was being blackmailed. Then, EJ manages to unlock the drawer.