Se-hee, played by Park Bo-young, is a shop attendant who navigates life independently alongside her younger sister, Jung-mi, portrayed by Kang Byul. Their circumstances are marked by the tragedy of their mother's death and their father's decision to pursue work in the United States, leaving the sisters to rely on one another. However, a misunderstanding creates distance between Se-hee and her boyfriend, Joon-hyuk, an IT college student played by Joo Won. In an effort to mend their fractured relationship, Joon-hyuk seeks Jung-mi's help, asking her to persuade Se-hee to reconcile. In exchange for her assistance, Jung-mi reveals her secret—she has been earning money to support their tuition by uploading viral videos. She particularly requests Joon-hyuk to download a video that has been blocked for its rumored curse, which is said to bring harm to those who view it.
As Joon-hyuk retrieves the video, he discovers it consists of 108 different clips that change each time they are watched. The content varies dramatically, touching on disturbing themes of witchcraft, as well as a troubling incident involving a middle-aged man and a drunken woman. After watching the video, both Jung-mi and Se-hee start to feel the unsettling presence of something supernatural. When Jung-mi sends the video to an internet artist, she unwittingly sets off a chain of horrifying events that culminate in the artist being crushed by an elevator, with the shocking footage of her demise later incorporated into the cursed video.
Meanwhile, Jung-mi becomes an internet sensation after an unexpected viral incident involving a stripping dance on a train, which further complicates her already fraught situation. The combination of her newfound fame and the constant feeling of being watched leads her into a spiral of paranoia and violence. In light of these troubling events, Se-hee seeks help from Joon-hyuk to place security cameras around their house to monitor Jung-mi's erratic behavior. One day, Jung-mi runs away to an abandoned house once owned by the man involved in the harassment from the video.
As Joon-hyuk investigates the case, he uncovers that the man was not a perpetrator as originally depicted; rather, he only sought to provide comfort to the woman in distress. Tragically, he took his own life due to public shame, and the resulting despair affected his entire family. His daughter, bullied because of this video, created the cursed footage that now haunts Se-hee and Jung-mi.
In a race against time, Se-hee, Jung-mi, and Joon-hyuk confront the horrors at the abandoned location, where they discover devastating truths, including the remains of the girl who recorded the harassment. They find and destroy the doll used for the curse alongside the flash drive containing the cursed video, hoping it will put an end to their ordeal. However, their relief is short-lived as the curse’s influence remains, resulting in the tragic deaths of Joon-hyuk and Jung-mi during their efforts to break free from the curse's grasp.
The story reaches its climax when Se-hee faces the vengeful daughter on a rooftop, leading to a tense confrontation where the daughter demands that Se-hee joins her in death. In a surprising twist, Se-hee survives the fall, but her victory feels hollow as she encounters reporters at the scene, laden with cameras and videos, hinting that the curse is far from finished and she may never escape its chilling grip.
