In the quaint town of Vernon, a chilling series of events took place on the nights of October 27, 29, and 31 in 1987. On these fateful nights, three teenage girls—Tiffany Clark, Marisa Song, and Heather Hernandez—met a horrific end at the hands of the notorious Sweet 16 Killer, each brutally stabbed 16 times on their 16th birthdays.

Fast forward to the present day: teenager Jamie Hughes is looking forward to a Halloween concert with her friend Amelia Creston, while her mother Pam Hughes decides to stay back and hand out candy. Unbeknownst to Jamie, Pam shares a tragic connection with the victims, having been friends with them, and that very night, she becomes the killer’s next target, brutally slain in a shocking twist.

In her time of mourning, Jamie discovers a sinister message that Pam had hidden—a note from the killer reading, > “You’re next, one day.” Determined to alter fate, Jamie jumps into a time machine she and Amelia have been tinkering with, hoping to travel back to 1987. In a world where Pam and her friends were ostracized for their bullying, Jamie adopts the guise of an exchange student from Canada, seeking to change the course of history and save her mother.

As Jamie blends into the past, she seeks help from Lauren Creston, Amelia’s mother, and Doug Summers, who is now the principal of her school. Attempts to intervene at a party hosted by Tiffany fall short when the timeline unfolds tragically—Pam’s past reality connects with painful new experiences as Jamie struggles to protect her mother and her friends. Despite her best efforts, Heather becomes the latest victim, leading Jamie to realize the precarious nature of time and destiny.

On Halloween night, the tension escalates as they gather at an amusement park where Lauren is constructing a new time machine for Jamie’s return. Meanwhile, in the present day, Chris Dubasage assists Amelia in retrofitting their machine and uncovers the reality of shifting timelines. The group ingeniously lures the Sweet 16 Killer into a haunted house confrontation, where Kara Lim, the sheriff, impales the attacker with a scythe.

However, the real drama unfolds as Doug is unmasked as the initial killer, fueled by revenge for his girlfriend Trish’s demise—a tragedy linked to Pam. The narrative thickens when Jamie learns that Chris from the present is additionally entwined in this dark tale, having deceived everyone for the sake of his podcast ambitions. In a climactic battle, Jamie’s resourcefulness shines as she confronts Chris in the time machine, where she ultimately prevails, sending him spiraling into oblivion.

By the time Jamie returns to the present, she discovers that time has been rewritten in her favor. Pam lives, and the twist of fate has gifted Jamie, now Colette, with an older brother in a timeline long thought set in stone. The threads of past and present intertwine spectacularly, revealing the costs and consequences of tampering with time.