Madison Penrose, a wealthy and self-centered high school student, is gearing up for her much-anticipated Sweet 16 and decides to host the party at the Roller Dome, a roller-skating rink with a notorious and violent past. Though her father voices serious concerns, Madison's determination wins out. A flashback reveals the terrifying history: Charlie Rotter, the rink’s owner, murdered two teenagers for insults, dismembered four others, and only stopped when his six-year-old daughter, Skye, alerted the police, leading to his arrest. A later news report claims Charlie was believed dead in a bus accident on the way to prison.
Ten years pass, and Skye Lauren McKnight, now a high school student, dreams of becoming an artist while living with her aunt, Sarah. Yet, as the daughter of a serial killer, she endures relentless ridicule from Madison and her circle. When Skye crosses paths with Brigg Jenner [Chris Zylka] and his best friend, Derek McNamara, the informal chemistry between Skye and Brigg becomes clear. Their flirtation is observed by Madison’s circle, and Olivia Wade, one of Madison’s closest friends, hurries to tell the others. The plan to punish Skye is hatched, and Madison’s threats soon spill into the hallways of their school. After a run-in in the locker room where Skye finds her locker smeared with red paint and cruel notes, Lilly McFadden—a friend who secretly dislikes Madison—encourages Skye to seek revenge, though Skye initially refuses. The tension escalates when Madison and her friends confront Skye after school, taunting her about Brigg’s interest in someone else.
Brigg, however, remains drawn to Skye and agrees to take her home after a casual encounter in which he asks her out. The next day, Madison hands out party invitations to her friends and intentionally plops one into Brigg’s hands to provoke jealousy. Skye, at her home with her best friend Derek, becomes entangled in the plan to crash Madison’s party at the Roller Dome. Derek mentions crashing the party, but Skye worries about the dangerous setting. Still, Brigg arrives and says he has to cancel the date because Madison expects him at the party, prompting Skye to consider ending things. Despite that, Brigg reassures her and pledges more time together. That night, Skye and Derek decide to crash the event, slipping in through a back door after Lilly unlocks an entryway, though Skye notices another door left ajar.
Inside, the party planner, a much older man who makes unwanted advances toward Madison, is fatally attacked with a spear by Charlie Rotter, who has indeed survived the bus crash. Derek, who tries to charm several attendees, encounters Lilly and, after a strong moment, they connect in the basement. When Kevin, Madison’s ally, confronts Derek, the situation spirals as Derek uses the party’s mood and a scare tactic—utilizing Charlie’s mask to intimidate Kevin—only to be overpowered. Madison witnesses Skye laughing with Brigg, intensifying her jealousy.
A drunken Lilly overhears Derek’s distress and frees him, and the two grow closer. That night, Skye glimpses her father on a balcony and discovers it is Kevin in disguise as a cruel prank; Skye’s heart sinks as the real Charlie violently attacks Kevin. On the party’s other front, Chloe and Olivia plot a prank involving a fire extinguisher; Chloe convinces Olivia to assist, but Olivia’s plan falters when Charlie grabs the extinguisher and bludgeons Chloe to death. In a separate tragedy, Lilly discovers Madison’s birthday present, a silver BMW, outside the roller rink and carves “Happy Sweet 16” into the paint, not realizing Charlie is hidden in the car and waiting to strike. A body count rises as Olivia is found beheaded by Charlie, and the party descends into chaos. The guests flee while Madison’s father delivers a heartfelt birthday speech.
As Madison confronts Skye and tries to mend fences, Charlie appears and blocks the exits. The party spirals into a nightmare as the killer dispatches more of Madison’s circle, and the bewitching tension between Skye and Madison culminates in dangerous standoffs. Skye ultimately frees herself and tries to rescue Madison, but Madison’s selfish cruelty continues. In a final grim confrontation, Skye lures Madison away and locks her inside the basement with Charlie, severing Madison’s escape and letting justice unfold in the depths of the Roller Dome. After the police arrive, Brigg regains consciousness, only for Skye to drive away in Madison’s car as the authorities close in, leaving Charlie missing.
In the days that follow, Brigg wakes in a hospital bed to find Skye nearby. But instead of reconciliation, he experiences a nightmare in which Skye stabs him as he screams, only to wake to a nurse who calms him and reveals that Skye has not been located in days. A folded piece of paper sits on a nearby desk: a self-portrait of Skye, hinting that she visited Brigg while he slept. The portrait leaves viewers with a chilling sense that Skye’s quiet vengeance may not be finished—and that the lines between victim and perpetrator have become increasingly blurred.
