Olivia Barron is a college student who always puts others' needs before her own. She plans to spend spring break building houses with Habitat for Humanity, but her best friend, Markie Cameron, convinces her to join their circle of friends in Mexico. At a bar, Olivia meets Carter Boyle, who invites the group to party at an abandoned church. There, Carter introduces a game that looks like a supernatural version of truth or dare and warns that they must do whatever the game asks or they will be killed.
Back at school, unsettling visions push Olivia toward making a choice in the game. She blurts out that Markie has been serially unfaithful to Lucas Moreno, while other confessions echo through the group. The stakes escalate when Tyson Curran dies after lying during a turn, and the group uncovers a grim thread of history online about a woman named Giselle Hammond who lit a woman on fire in Mexico while playing truth or dare. Giselle reveals that one friend, Sam Meehan, got drunk and trashed the church, and when they got home, the game continued. Only she and Carter survived: Carter had been dared to bring in more players to buy time for their own next turns. Giselle’s truth prompts the revelation that she has been dared to kill Olivia, and she opens fire—but Olivia’s friend Penelope Amari dives in front and dies instead. Giselle, unable to face the consequences of her dare, is driven to kill herself.
Olivia is then dared to have sex with Lucas. During their encounter, Lucas admits that he cares for her but loves Markie, complicating Olivia’s feelings. The couple drives to Tijuana and encounters Inez Reyes, a former nun at the church who cannot speak. Through writing on paper, Inez explains how she summoned a demon named Calux to save herself from an abusive priest, only for Calux to keep a cruel game of truth or dare running and to kill her friends. She trapped Calux by ritually cutting off its tongue and sealing it in a pot, a trap the group later suspects Sam may have broken. To stop Calux, they must locate him.
Brad Chang is forced to threaten his father with a gun, and a gunshot from an approaching officer ends Brad’s life. Olivia learns that Carter and Sam are the same person, a twist that reframes much of what they have endured. Olivia musters her courage to speak the truth about Markie’s father, who sexually assaulted her and killed himself when she told him the abuse would end with Markie’s life improved. Markie, hurt and angry at first, eventually forgives Olivia and reminds her that she is not to blame because her father had once been suicidal as well.
The trio—Olivia, Markie, and Lucas—track down Sam and force him back to the ruined church. As Sam undergoes the ritual to trap Calux, Lucas faces a deadly choice: kill Olivia or Markie. He refuses, Calux possesses him, and he kills Sam and then himself. When it is Markie’s turn, Olivia urges her to refuse a dare. Calux possesses Markie, and Olivia counters by forcing Calux into the game himself, compelling him to tell the truth: there is no way to escape the game alive with Sam dead. To survive, they must add more players and delay their next turn. Olivia uploads a video briefly warning viewers about the game and its rules, then poses a final gambit: she asks a round of “truth or dare” that drags in anyone who hears the phrase, effectively extending their improvised delay and giving them a fighting chance to outlive the game.
