The Escape Game by Tamara Moss and Marissa Meyer

Here is a summary with spoilers for The Escape Game by Tamara Moss and Marissa Meyer

During the Season Four finale of a televised escape-room competition, Sierra Angelos discovers the body of her older sister Alicia hidden inside a coffin prop during a vampire-themed challenge. The discovery shocks the contestants and production staff, and Alicia's murder remains unsolved. 

Six months later, despite the murder, the show goes on, and the Game Master and his assistant start looking for their next contestants. Sierra returns for Season Five alongside Carter Kelly, a highly ranked puzzle solver known online as Kick It Carter; Beck Matheson, a homeschooled escape-room designer with synesthesia; and Aditya "Adi" Parvesh, a quiet teenager hoping the show might help him reconnect with his estranged father. During the opening challenge, the contestants uncover a hidden message spelling Alicia Angelos, the first clue left by an anonymous figure known as the Real Game Master. It spooks a few of the other contestants, but it only spurs Sierra along; while still seen as a supsect in her sisters death, Sieera is admit about finding out who did it. 

As the season progresses, the Real Game Master posts coded messages and evidence online, encouraging fans to investigate Alicia's death. Team Helsing, the name Sierra chooses for her team (which alludes to her sister), becomes the target of threats connected to the murder. Beck discovers a cow's heart and threatening note, Carter's drink is spiked at a party, and additional coded clues appear throughout the competition. During one incident, a masked figure traps the team inside an industrial freezer. While they are trapped, Sierra explains that she and Alicia grew up in foster care after their parents died and reveals Alicia's instruction to look "under the terrace" if anything happened to her. After being rescued, the team becomes determined to solve the murder themselves.

The team continues advancing through the competition while gathering evidence. During one challenge, images of possible suspects appear, ending with Alicia's face. Later, Sierra realizes Alicia's clue refers not to a physical terrace but to Van Gogh's Café Terrace at Night painting hanging in the villa. Hidden behind the painting is a note in which Alicia reveals she was having an affair with Louis Augustus Russell, the show's Game Master, who was married to executive producer Ranielle Russell. Alicia also warns Sierra not to trust the Russells. Shortly afterward, Carter arranges to meet Louis but instead finds him dead beside what appears to be a suicide confession admitting to Alicia's murder. Police rule Louis's death a cyanide suicide and close Alicia's case, but the team notices inconsistencies and suspects he was murdered. Alicia espically is not happy with how things have ended, and still has questions about her sisters death. 

At the same time, Adi becomes involved in a separate conflict involving Ranielle. She offers him the chance to become the next host of the show if Team Helsing wins and pressures him to accept advance puzzle answers. Adi appears to cooperate but secretly uses the opportunity to access files connected to Sweetbrier Resort, a property owned by his estranged father, Victor Cunningham. Beck reveals that Sweetbrier sits on land that once belonged to his family and that Victor became wealthy after discovering buried gold there. Team Helsing performs well in the competition, but rival contestant Jarius releases a recording of Adi discussing puzzle answers with Ranielle. Although Adi explains he never used the answers and only accepted them to gain access to information, the team is disqualified.

After their elimination, the team continues investigating. Adi realizes Alicia's note contains a hidden scytale cipher. When decoded, the message reveals Alicia had been blackmailing Ranielle and intended to expose her publicly. Carter also examines Louis's confession and notices details proving it was forged, including handwriting inconsistencies and spelling patterns linked to Fitzy, the show's host. These discoveries convince the team that both Alicia's and Louis's deaths are connected and that the official explanation is false.

When Hitflix cancels the show, Team Helsing confronts Ranielle. She admits she knew about Louis's affair with Alicia and had tried to buy Alicia's silence by offering her a hosting position, but she denies murdering anyone. The team later breaks into the studio, where Vera, the show's social media manager, reveals that she has secretly designed the escape rooms since Season Two. Vera also reveals that she found Fitzy's shark tooth pendant near the location where Alicia's body was staged, though investigators dismissed the evidence because Fitzy had an apparent alibi.

Fitzy then arrives with a gun and confesses that he moved Alicia's body into the coffin, poisoned Louis, and forged the suicide confession. Soon afterward, Symphony Parvesh, Adi's mother, reveals she was the person who actually killed Alicia. Angry that Alicia had been offered a hosting job she wanted for herself, Symphony suffocated Alicia and stole her phone to create a false timeline. She stored the body inside the industrial freezer before having Fitzy transport it to the studio. The frozen storage altered the condition of the body and misled investigators about the true time of death, which was the key inconsistency the Real Game Master had challenged everyone to discover.

Fitzy and Symphony pursue Team Helsing through the remaining escape rooms as they attempt to escape. During the confrontation, Vera stabs Fitzy with a wooden stake, Beck is shot, and Adi solves the final puzzle by using the code "VERA" to unlock a hidden passage. The passage allows police officers to enter and stop the attackers. Symphony points a gun at Adi and fires, but Sierra intervenes and the bullet strikes a Dracula mannequin instead. Symphony is arrested, and Fitzy is taken away in critical condition.

In the aftermath, Carter organizes a fundraiser to help cover Beck's medical expenses, and Victor Cunningham's company fully funds it. Sierra visits Alicia's grave, while Beck recovers from a coma. Each member of Team Helsing receives a black envelope inviting them to Sweetbrier Resort. At the same time, Adi finally meets Victor Cunningham, who confirms that Adi is his son. The novel ends with the team being drawn toward Sweetbrier Resort, the mystery of the hidden treasure beneath it, and a new game that has only begun.