The Book Verity by Colleen Hoover begins with Lowen Ashley, a writer who is hired to write the final three novels in a bestselling book series because the author, Verity Crawford, is unable to do so herself.
On her way to a meeting with her publisher, writer Lowen Ashleigh witnesses the death of a man. She is helped by Jeremy Crawford, a good-looking stranger. They quickly bond and share their recent personal grief-filled experiences. Verity’s mother died of cancer recently. Both of Jeremy’s twin daughters died within six months of each other. They part ways, only to realize they are both on their way to the same rendezvous at Pantem Press.
Jeremy Crawford is Verity Crawford’s husband. The offer made to Lowen asks her to complete the books in exchange for a large sum of money. Lowen accepts the proposal and agrees to travel to Vermont to collect notes from Verity’s office. Lowen’s literary agent and previous lover, Corey urge her to be cautious given the strange nature of Verity’s car accident, which has rendered her immobile.
Lowen makes her way to Vermont. Crew, a five-year-old boy, is the only surviving Crawford kid. Uncomfortable, Lowen strives to settle in and get to work. She soon discovers a manuscript titled So Be It, which she misidentifies as Verity’s autobiography. It is actually a writing exercise in which Verity explores violent emotions to better understand characters. Lowen notices Verity staring at her as she reads and feels increasingly threatened by her presence.
The early parts of the autobiography focus on Verity’s pregnancy, which she attempted to abort with a hanger and terrible disdain for the twin daughters that Jeremy loved more than his wife.
Lowen is disturbed by the manuscript’s content and suspects Verity played a hand in her daughters’ deaths. Lowen learns about Verity’s twins, Harper and Chastin, and how she neglects them throughout the day while Jeremy is at work.
Lowen goes for a sleepwalk and wakes up in Verity’s bed. She tells Jeremy about a horrible event she had when she was 10 years old, which culminated in her mother’s neglect and a two-week psychiatric examination. Lowen is consoled by Jeremy. Jeremy installs a lock on the outside of Lowen’s bedroom door to calm his fears.
Lowen then reads about Verity’s dream in which Harper murders Chastin. As a result, Verity decides to kill Harper by forcing her to swallow her own vomit. Jeremy intervenes before she reaches what she wants to achieve.
Strange things continue to occur in the present day: Crew, Jeremy’s son, waves to his allegedly unconscious mother in the window, implying she is staring at him. Lowen believes she sees Verity at the top of the stairs, and Crew casually mentions speaking with his mother, prompting Lowen to wonder if Verity is truly as injured as everyone believes which she obviously isn’t.
Lowen resolves to complete the autobiography before deciding whether or not to tell Jeremy the truth about Verity. She learns that Chastin died during a sleepover due to an allergic reaction. Verity becomes certain that Harper was involved in her sister’s death. Lowen is briefly alone with Verity on her birthday, whom she confronts. Verity is immobile. Later that evening, Lowen advises that Jeremy place Verity in a nursing home to alleviate the strain of her care.
Things only get worse when Lowen reads the final chapter of Verity’s manuscript, in which she describes deliberately drowning her remaining daughter in a lake.
When Lowen is alone with Crew, she quizzes him about Harper’s death date. Crew slashes himself with a knife by accident. Jeremy drives him to the hospital for stitches, leaving Lowen alone with Verity. Lowen locks the door and installs a baby monitor in Verity’s room. She keeps an eye on the monitor and reads the final chapter of the text. Verity’s manuscript concludes with Jeremy doubting Verity’s role in Harper’s death. Verity considers suicide as a response.
Jeremy reappears. Lowen notices Verity on the floor of her bedroom on the baby monitor. She dashes upstairs to confront Verity once more. Jeremy grabs Lowen and orders her to leave. Lowen ultimately hands over the document to Jeremy and requests that he read it. Once he does, angered, Jeremy confronts Verity and threatens to call the cops on her. Verity blinks opens her eyes. Jeremy starts strangling her. Lowen interrupts him and proposes he murders Verity in the same way she attempted to murder Harper as a newborn. Verity is forced to choke on her own vomit by Jeremy. Lowen and Jeremy swear they will never talk about what happened.
Seven months after Verity’s death, a pregnant Lowen, Jeremy, and Crew return to Vermont, where Lowen discovers a letter from Verity to Jeremy in which Verity describes how her manuscript was a writing exercise called antagonistic journaling that helped Verity get into the heads of her wicked characters. Verity describes how Jeremy discovered the book in the days after Harper’s death and subsequently arranged a vehicle accident to kill her. Verity confesses to looking at Lowen, locking her in her room, and plotting to flee with Crew. Lowen chooses to destroy the letter in order to keep Jeremy at peace. She pledges to keep the secret till she dies.