The Inheritance Games begins with its protagonist, seventeen-year-old Avery Grambs, playing her daily game of chess with Harry, a homeless man, in the park. She wins and rushes off to school. Once there, the principal calls Avery to his office and accuses her of cheating on a test. He implies that her home life, including the death of her mother and the barely-scraping-by lifestyle that she and her older half-sister, Libby, lead, may be the cause of her behavior. Innocent, she demands to retake the test. When Avery gets home from work, she finds that Libby has been baking, a sign of something bad. Libby’s on-again, off-again boyfriend, Drake, makes his way into the kitchen, and, because of his cruel attitude, Avery decides to live in her car. When the principal calls Avery to his office again a few days later, she assumes that her new test has been graded. Instead, she meets a boy in a suit who introduces himself as Grayson Hawthorne. He explains that his deceased grandfather, billionaire philanthropist Tobias Hawthorne, named Avery in his will, and she must be present for its reading.

When Avery and Libby arrive in Texas for the reading of the will, a young woman named Alisa Ortega introduces herself as their liaison to the law firm that represents the Hawthorne estate. They travel to the Hawthorne House, a sprawling mansion on a hill. Grayson meets them in the foyer, and his youngest brother, Xander, pops out of a coat closet that leads to a secret passageway. Skye, the boys’ mother, and Zara, her sister, come to inspect Avery and suggest that Grayson is “the heir apparent.” Once the rest of the household, including the remaining Hawthorne brothers Nash and Jameson, gather in the Great Room, lawyers begin reading Tobias Hawthorne’s will. While he left some money to his family and long-time employees, the vast majority of his fortune goes to Avery. Avery is stunned, and the Hawthornes are extremely angry. The only stipulation in the will is that Avery must live at Hawthorne House for one year, or her inheritance will go to charity. 

Despite her reservations, Avery moves into Hawthorne House. Unfortunately, the transition is far from smooth as Drake, upset with Libby, tells the press about Avery’s inheritance. The Hawthorne boys also distrust her, although Jameson soon insists that she is the key to his grandfather’s final puzzle. Avery initially dismisses this idea and tries to focus on adjusting to her new life, navigating a new school, and staying in touch with her best friend, Max. Despite warnings from Thea, a classmate who is particularly familiar with the Hawthorne brothers, Avery’s curiosity ultimately gets the better of her and she starts trying to solve Tobias Hawthorne’s clues. She reads the letters that he left his grandsons, and they lead her to the house’s libraries where she, along with Jameson and Grayson, search for a book with a mismatched cover. As they work, Avery begins to learn about a girl named Emily who recently passed away. 

The longer that Avery is in Hawthorne House, the more she learns about the complex relationships and traumatic events that plague the family. Tobias Hawthorne changed his will twenty years prior to include the middle name “Tattersall” after his son Toby died in a fire, and he rewrote it a year ago to give everything to Avery. A clue they find in the library alerts Avery to the existence of a unique will written in red ink, and reading the Red Will indicates that the boys’ middle names are her next clue. Once Skye reveals that Tobias Hawthorne chose his grandsons’ middle names, Avery discovers that they correspond to places or things on the property. Her search, which she pursues with the help of Jameson, comes to a halt when Drake brings paparazzi to the Hawthorne House gates and a shooting occurs while Avery and Jameson are in the estate’s Black Wood.

In addition to her new fear for her life, Avery struggles to comprehend her relationships with the Hawthorne brothers. Learning about Emily’s final days sheds some light on the boys’ behavior, as she pitted Jameson and Grayson against each other. Avery refuses to let their competitive nature get in her way, however, and she pushes forward and realizes that a number is hidden at each location that corresponds to the boys’ middle names. Avery has found all but one when the time comes for her to attend her first formal event alongside the Hawthorne family. Preparing for the charity gala puts her in danger again as her attacker, who Oren discovers is Drake, attempts to run her car off the road. When Avery finally arrives at the event, the boys are shocked to see that her stylists dressed her exactly like Emily, per Thea’s request. Seeing Avery’s regret brings Jameson to apologize to her and the rest of the Hawthorne boys to warm back up to her. As she leaves the gala, Xander suggests that Avery have a helicopter fly her over the Black Wood.

Flying over the Black Wood with Jameson and Grayson in tow allows Avery to find the final number, and she realizes that the clue is the date October 18th, her birthday. The boys also explain that Emily died that day, insisting that this is the end of the puzzle. Refusing to believe that she was chosen purely for her birthday, Avery keeps searching and finds a purple octagon with a note hidden behind Tobias Hawthorne’s portrait. With Xander’s help, she connects this clue to the stained-glass window in the Great Room that, when manipulated, reveals a secret tunnel. Inside, they reach a wall that opens when Avery looks into a facial recognition device, but they cannot open the door behind it without the handprints of each Hawthorne brother. Once Xander convinces his brothers to come down, they open the door and find a box with letters for each of them. Avery’s has a sugar packet inside, and it brings back a childhood memory of meeting Tobias Hawthorne while at a diner with her mother. She later searches his desk and discovers that he kept a detailed file on her life, emphasizing that he cared about her. Xander’s letter instructs him to find Tobias Hawthorne II, Tobias Hawthorne’s deceased son, who Avery has just realized is actually Harry, the homeless man with whom she used to play chess.