During a senior calculus class at Covington High, a shocking incident occurs when senior student Katelyn Ogden unexpectedly explodes, showering her fellow classmates and the entire classroom in gore. Subsequently, law enforcement takes the class into custody amidst an investigation, ruling out an attack yet failing to discover the cause behind this mysterious explosion.
While in custody, senior student Mara Carlyle voices her concern that such a catastrophic event could recur, a notion that resonates deeply with her classmates. Shortly after, she receives an anonymous text from someone claiming to have harbored feelings for her for years. To the surprise of Mara, when she asks for no inappropriate photos, the texter replies with a bizarre image of Richard Nixon.
Mara resides with her parents, Angela and Charlie. Following Katelyn's funeral, Mara indulges in mushrooms bought from school dealers, Jenna and Joe, and shares a calming tea with her close friend Tess. It’s during this time that fellow student Dylan Hoevmeyer reveals that he’s the admirer who has been texting her. Dylan reflects on life and its fragility, voicing his concerns about the possibility of further explosions occurring, thus motivating him to take decisive action.
As their romantic relationship blossoms, they attend a school football game and a house party, both of which end abruptly when another student, [Perry Love], and drink server Cranberry Bollinger explode, triggering chaos among attendees. Classes are eventually suspended, leading students to dub the phenomenon "The Covington Curse." Dylan, who drives a milk truck van, gets caught up in the frenzy, which draws the attention of various government agencies. This leads to the assignment of FBI Agent Carla Rosetti on the case, who enlists Mara and Tess for assistance.
As they explore possible drug connections to the explosions, Mara takes a ride with the Dalton twins, the school dealers. Their drive takes a horrific turn when they explode, causing their car to crash. Dylan arrives on the scene to comfort a shaken Mara, just as federal agents clad in protective suits detain them. The entire senior class is placed under observation while the government engages in developing a "Snooze Button" pill purportedly designed to "cure" the students, amidst an alarming number of additional explosions as multiple medications are experimented on them.
Determined to live as if every day might be their last, Mara and Dylan embark on a hedonistic lifestyle, sharing intimate moments and dancing to iconic 80s music in an old barn. As classes resume, town residents begin to harbor fear towards the students. In an inadvertent slip, Agent Rosetti confides in Mara that more explosions could still be on the horizon. During a school seminar aimed at demonstrating the effectiveness of the pill, catastrophe strikes again when another student explodes, setting off a chain reaction of further explosions, leading to widespread chaos and terror across the classroom.
In the midst of the pandemonium, while attempting to escape, Mara and Dylan become separated. Although Mara easily makes her way outside and reunites with Dylan, tragedy strikes as he explodes right before her eyes, leaving her injured. Overcome with grief and despair following Dylan's death, Mara turns to alcohol, which destroys her relationships with her parents and Tess. In an instance of drunken recklessness, she accidentally shatters Agent Rosetti's car window with a stolen whiskey bottle. Meanwhile, rumors circulate online insinuating that Mara may be linked to the Covington Curse, given her presence during each explosion.
At the combined graduation and prom ceremony, Mara reconciles with Tess, who announces that she is leaving town for a beach house that very night and invites her to join. Despite feeling like a curse, Mara offers a casual apology to the attendees for her supposed part in the explosions, only for others to voice their confessions, attributing their problems as causes as well. Post-event, Mara visits Dylan's grave and has a heartfelt conversation with his mother, Denise, who encourages her to move on with her life. Taking her advice to heart, Mara mends her relationships with her parents and strives for sobriety.
Post-explosions, the next batch of "Snooze Button" pills appears to function effectively, ending the explosions and leaving 31 students deceased. Consequently, Covington High is shut down by authorities and marked for demolition. Gaining possession of Dylan's milk truck, Mara, with her parents' support, prepares to move into the beach house with Tess, a long-held dream since childhood. The film concludes with Mara urging viewers to cherish life, reflecting on the thought, "[What] the fuck else can you do?"
