Olivia Barron, a college senior, is planning to spend spring break working for Habitat for Humanity. Her best friend Markie Cameron, whose father had committed suicide earlier in the year, prevails upon Olivia to spend their last spring break partying together. Along with Markie’s boyfriend Lucas and their friends Penelope, Tyson, and Brad, they travel to Mexico. While there, they run into Ronnie, an obnoxious fellow student. At a bar, Olivia meets a man named Carter who invites them all to go drinking at an abandoned church nearby. While there, Carter suggests that they play a game of truth or dare. During the game it is revealed that Olivia has a secret crush on Lucas, which angers Markie. Carter ends the game by admitting that he tricked them into playing a supernatural version of the game and warns them to do whatever the game asks or they will die.
Back at school, Olivia sees hallucinations calling on her to pick truth or dare. After being harassed by the aggressive hallucinations she picks “truth” and blurts out that Markie has been serially unfaithful to Lucas. The other friends disbelieve her explanation of a cursed game until they learn that Ronnie was forced to kill himself after failing to complete a dare. Lucas gets messages from the game until he picks “truth” and admits that he has always had feelings for Olivia. Markie gets a message from the game and is forced to break Olivia’s hand. Brad is then forced to admit to his father that he is gay.
Tyson, a pre-med student, has the next turn and is ordered to tell the truth about forging drug prescriptions during an admissions interview. Disbelieving the reality of the game, Tyson denies the charge and is killed. A distraught Penelope, who has been drinking heavily, is then forced to walk along the eaves of a house and nearly falls to her death. The group discovers a story online about a woman named Giselle Hammond who lit a woman on fire in Mexico while apparently playing truth or dare. They arrange a meeting with Giselle through social media.
Giselle reveals that her group of friends were playing Two Truths and a Dare in the same church. One person in her group, Sam, got drunk and began trashing the place. When they got home, the game somehow continued and only she and Carter survived. Carter was dared to involve more players into the game to give themselves more time before it became their turn again. Giselle reveals that she has been dared to kill Olivia and tries to shoot her, but Penelope dives in front of Olivia and is killed instead. Having failed at her dare, Giselle is forced to kill herself.
It is then Olivia’s turn, and she chooses dare and is dared to sleep with Lucas. While they have sex, Lucas is charged with Truth and admits that he is still in love with Markie and not Olivia. Meanwhile, Markie, all alone, also picks truth and admits that she too has been contemplating suicide.
Olivia and Lucas drive to Tijuana and meet Inez Reyes, a former nun at the church who cannot speak. By writing on paper, Inez tells them of how she summoned an ancient demon named Calux who possessed the game of Truth or Dare to save herself from the sadistic priest. However, Calux kept the game going and killed all her friends. She trapped Calux with a ritual including cutting off her tongue and sealing it in a pot. The group realize Sam must have broken the pot and released Calux, and to trap him, they need to find Sam.
Brad is dared to threaten his father with a gun. As he does so, he is shot and killed by an approaching officer. At the precinct, Olivia learns that Carter and Sam are the same person. Olivia is then dared to speak the truth. Olivia tells Markie that the night her father killed himself he had sexually assaulted her and she had wished he was dead. Markie forgives her friend, noting that her father had been suicidal for a long time.
Olivia, Markie, and Lucas find Sam and force him at gunpoint back to the ruins of the church in Mexico. Lucas’s turn comes as Sam goes through the ritual to trap Calux. Lucas is dared to kill either Olivia or Markie. When he refuses, Calux possesses him and forces him to kill himself, although first Calux has him kill Sam, so Sam cannot complete the ritual. When Markie’s turn comes, Olivia tells her to choose dare, then refuse to complete the dare. After that, Calux possesses Markie, at which point Olivia forces Calux into the game by asking him to pick truth or dare. The demon is forced to tell the truth that there is no way they can make it out of the game alive because Sam is dead. They’ll die unless they add more people to the game to delay their next turn.
Olivia uploads a YouTube video, in which she briefly warns viewers about the game and its rules. She then asks “Truth or Dare”, involving whoever hears the phrase into the game, delaying her and Markie’s next turn, but effectively dooming anyone who watches it in the process.