During Avery’s 18th birthday celebrations, all of the Hawthorne brothers are in various places around the world, and Alisa is trying to convince Avery to put her money in a trust fund, as well as to plan a huge birthday party, which Avery does NOT want to do. Once the brothers get back from their endeavors, Jameson plans a private but extravagant birthday party for Avery, which consists of a hot air balloon ride, a massive dance floor, slow dancing on the beach, and only with close friends and family.

When Grayson and Avery were talking about the inheritance, Oren came to them stating that there’s someone at the gates named Eve. Avery is the only one who knows about Eve, but has never seen her, and Eve looks a lot like the Hawthorne’s close friend who passed away, which would really hurt the brothers. Jameson is very emotionally distressed after seeing Eve, but she then reveals that Toby has been kidnapped by an anonymous person and that they have to help find him, Oren sends a search party looking for him and or suspects, while Avery and the brothers also begin ruling out people such as Avery’s grandma and Skye Hawthorne.

Rebecca meets Eve for the first time at the house, but it is upsetting because she looks a lot like her dead sister. While they continue looking for Toby and his captor, they begin getting letters from his captor; one includes a photo of Toby with yesterday’s news, proof that he’s alive. They rule out Skye and Avery’s grandma as his captor. Avery receives a package from Tobias for when she meets Eve, meaning he knew about her. The bag includes a bunch of seemingly random items, but Avery knows better than to assume that they’re trash, so she begins to see how she can use them.

Avery and Jameson try to find out what “Don’t breathe” means after they find it in a chess piece. After failing to figure out what the message means, Oren brings in another package from Toby’s captor, this time including a timer ticking down to an unknown event. They keep trying to solve the puzzles, but now there’s media circling that Jameson and Grayson killed Emily, which Xander calls an excuse to hold them back while the timer keeps going. Max helps them figure out that the seemingly random code to unlock the box is actually a Bible reference to the book of Luke, chapter 15, verses 11-32, “The Parable of the Prodigal Son”. Once the timer goes off, “Luke” calls, and Avery explains the whole story to him. After the phone call, they continue to wonder who Luke could be.

Avery and Grayson rule out Zara’s estranged husband as Toby’s captor, but go to Nan to find out anything about Tobias’s family, who all get ruled out. They continue investigating Tobias’s relationships until they come across “The List”, which includes a file of every single person who could be a possible threat to Tobias. Avery, the brothers, and Libby look through every file, trying but failing at finding any possible matches. Avery goes to talk to Xander about his father, which Xander doesn’t really want to. Avery goes to complete one of the puzzles left for her, but first she finds Grayson. He talks to Avery about how he was supposed to be the best before rudely dismissing her. Avery gets in the pool with the plate left in the satchel. After placing it over her eye, the bottom of the pool became a chessboard; she flipped over the tiles corresponding to the Queen’s Gambit, revealing a small package with a photo of 3 ladies, dated 12-19-73 in Marguex, France.

Xander decides to host karaoke, but Grayson doesn’t show up, so Jameson and Avery go to find him in the next room. Avery and Grayson go to the wine cellar to solve the image, and after Grayson finds a specific wine, they use the steamer from the satchel to remove the label; on the back is a drawing of a single crystal that could be found on one of 18 chandeliers in Hawthorne House. Avery, Grayson, and the Hawthorne brothers find the crystal and a note that says, “Don’t trust anyone.” Avery uses this note to pin suspicion on Eve, which the boys deny. They go to Mallory’s house, and seeing Eve brings back memories of Rebecca’s mistreatment. Avery discovers that Tobias issued a non-working patent with Vincent Blake, then very shortly after created a working patent that won him his fortune; with this, Toby’s captor reveals himself as not Luke, but Vincent Blake. Avery goes to talk to Nan, who tells more details about Tobias and Vincent’s relationship, like how Vincent’s sons took a liking to Alice, Tobias’s wife, and assaulted her; this is when Tobias released the patents.

Eve runs away to find Vincent; Grayson tries to follow, but Jameson stops him for an urgent conversation. Jameson locks Avery up in a secret room, telling her that he’s going with Grayson to find Eve and that Grayson would keep trying to find Emily until he hurts himself. Avery eventually breaks out, finding Xander, Thea, and Rebecca. Xander tells Avery that his father worked for Vincent Blake, so Avery has the idea to go to Isaiah Alexander’s mechanic shop. Isaiah tells the crew about how a pattern of weird things started to form, whether it was people going missing or tragic “accidents”, and how the seal they’ve been trying to decode the entire time is actually the Blake family seal, and rumor has it that whoever has one of the 5 seals gets a stake in Vincent Blake’s will, or about 100 million dollars, and that Vincent’s son is named Will Blake. Avery makes a connection to the poem that Toby put in a book in his wing, “The Poison Tree” by William Blake. Rebecca makes a note that another nickname for William is Liam, the name of the man who assaulted Mallory, who is Toby’s mother, making Toby Vincent’s grandson. Avery makes another accusation that Eve is not being trustworthy; this time, Jameson caught on.

Avery and Grayson go to the cottage where Grayson and Eve are. Jameson took Grayson outside for a chat, but Eve followed. Avery made a realization: Eve was just being used by Vincent as bait so he could get to her. After being forced out by Mrs. Laughlin, Grayson exploded to Avery, while she continued to try to get him to understand why Eve isn’t trustworthy, but he left angrily. After rereading “The Poison Tree”, Avery thinks back to Eve’s reaction; she began looking for evidence, for the body of Will Blake. Avery found her way to the chapel, as it was the first thing built after Toby’s birth. There, she unlocked the altar, but no body was found- just an inscription from Toby reading “I KNOW WHAT YOU DID, FATHER.” The only thing in the grave was a USB. After grabbing the USB, Eve appears in the chapel, pointing a gun at Avery, trying to get the USB. Oren pinned her down after she put down the gun. Grayson arrived in the chapel as well. Eve begged for the USB, but Grayson didn’t give in. Grayson admits to being in love with Avery, but knew she loved his brother. He gave her the USB, which should make the other one she got in the satchel audible. The voice recording told Avery that Tobias chose her because even if she dies trying to fight Vincent, she has nothing to lose. They receive yet another package from Vincent, this time including a bunch of clear sheets that, when lined up, reveal a photo of Alisa on the floor, knocked out. Jameson and Avery go to the hedge maze, the other spot a body could be hidden. After looking for a bit, Jameson finally says, “Dig here.”

Avery and Jameson find a shaft with more of Toby’s scriptures; Mr. Laughlin finds them, but Rebecca gets him to reveal what actually happened to Liam Blake. Turns out that once Tobias saw Mallory being assaulted, he got really mad and restrained Liam. Mallory was also really mad and picked up a brick and banged him in the head repeatedly. He died before they could get him medical attention. After finding the remains, Avery gets a call from Alisa explaining that Grayson is the one who’s captured, not her. Avery calls the authorities to tell them about the remains, then calls Landon to create the perfect publicity stunt to explain the body. Avery plans a press conference right outside Vincent’s house to play him in order to get Toby back. Avery goes to the property to orchestrate her plan and gets in the property easily because she’s in possession of one of the seals. Eve tells Vincent all about how Avery was involved with Sheffield Grayson’s death, adding more stress over the future. Avery challenges him to chess; whoever wins gets something they want. Vincent turns this into more of a tournament: 3 games, Avery-Eve, Avery-Toby, Toby-Eve; depending on the number of games they win, they win different things. Toby let Eve win; Toby lost against Avery, meaning that Toby had to change his name to Tobias Blake and had to stay on the Blake property. Then Avery let Eve win, meaning she got all 5 seals, but Grayson was still released. Avery calls for one last game so Vincent doesn’t reveal anything about Sheffield Grayson’s death.

During the final game, Vincent realizes how much he underestimated Avery’s chess skills and loses the game. For the final time, Avery went against putting her money in a trust and threw the document into one of the fireplaces. On the night of Avery gaining the inheritance, they have a massive party where each hour, the party rotates to a different activity until midnight when she’ll gain the inheritance. At midnight, they turn on the 24-hour news channel where they announce that Avery is giving away 94% of the inheritance to charity. With the money, she also buys Libby a truck so she can open a cupcakery. One year later, Avery adds the nook to the Hawthorne House as the first of her yearly expansions. Grayson dropped out of Harvard, Jameson is traveling the world with Avery, Xander is working as a mechanic with his dad, Nash works as Libby’s cupcake tester, as well as them getting engaged, and Avery is going to travel and go to UConn with a major in actuarial science, and planning a yearly puzzle contest with a huge money prize open to the public called the Grandest Game.