Four high school girls—Eun-Joo, So-Hee, Yoo-jin, and Eun-young—pledge to die together that night, a vow that hangs heavy over the campus as the clock ticks toward nightfall. Eun-Joo leaps from the roof of the school, a tragedy that is witnessed by her sister Jeong-Eun, who later recalls the fall in a world that suddenly feels crowded with questions and blame. The following day, So-Hee confesses in the school office that she was on the roof with Eun-Joo when she jumped, a revelation that instantly fractures friendships and stirs up rumors that swirl through the hallways.
As the rumor mill churns, paranoia takes root among the students and the truth begins to fray at the edges. So-Hee grows despondent, while the others cling to separate memories that may justify or condemn Eun-Joo’s decision. Jeong-Eun confronts So-Hee about the rift, but So-Hee insists she doesn’t know what happened. A tide of whispers accuses So-Hee of causing Eun-Joo’s death, and another rumor suggests that Eun-Joo took her own life because she was pregnant. The drama shifts to Eun-young, who endures a brutal night at home where her father lashes out because of her grades, and the next day she pleads with Yoo-jin to let her sleep at her house.
So-Hee is haunted by flashbacks of the friendship she once shared with Eun-Joo, and a growing guilt gnaws at her. Joo-yeon tells So-Hee that she is to blame for Eun-Joo’s death because she kept Eun-Joo at arm’s length. The tension escalates when Joo-Yeong is killed by Eun-Joo, a revelation that complicates loyalties and deepens the sense that something otherworldly or dangerous is at play.
Eun-young begins to glimpse Eun-Joo’s ghost, a haunting that unsettles her and unsettles the entire group. So-Hee discovers a dismembered body in a classroom locker, an ominous clue that points to the violence and secrets simmering beneath the surface. Eun-young shares a chilling detail: Eun-Joo had promised she wouldn’t kill any of them if they would confess, a condition that weighs on the four as they navigate fear and guilt. Later, Yoo-jin and So-Hee glimpse Eun-young on the roof and plead with her not to jump, but she does, claiming relief from an abusive home and a sense of fearlessness about the future she’s leaving behind.
In a church, So-Hee seeks absolution and Yoo-jin follows, while a flashback reveals So-Hee with her boyfriend, Ki-Ho. The truth about Ki-Ho and the past between Yoo-jin and So-Hee surfaces: Yoo-jin used to date Ki-Ho, and she helped drive a wedge between So-Hee, Eun-young, and Eun-Joo. In the present, Yoo-jin vents fear about academic pressure, insisting she must stay ahead to beat So-Hee, and Eun-young admits the abuse she endures at home. The trio resolves to pretend to jump, a perilous game designed to outmaneuver one another’s pride and fear.
Tensions peak when Yoo-jin ties a microphone around So-Hee’s neck and suspends her in a deadly hold, only for Eun-Joo to storm in and strangle Yoo-jin in a moment of furious intervention. A flashback further reveals Eun-Joo’s wish to die together with So-Hee someday, while So-Hee confesses her pregnancy and swears she will join Eun-Joo in death to protect the baby. On the roof, the four girls meet as planned, hands linked in a fragile ritual. But the moment of truth fractures as Eun-young and Yoo-jin step back from the planned jump, and So-Hee is left to face the consequences of a pact that never truly held.
What follows is a haunting resolution: Eun-Joo smiles and tells So-Hee that she missed her and wanted to return, yet fears she would scare So-Hee, prompting Jeong-Eun to grab So-Hee’s hand and force an impossible choice. Eun-Joo’s message lingers—So-Hee must stay to care for Jeong-Eun—and So-Hee ultimately assumes a new, protective role as Jeong-Eun’s older sister, a reversal that binds the survivors in a different, stubborn form of loyalty.
In the aftermath, So-Hee chooses to raise the baby, while Ki-Ho has moved on with another girl, leaving the future unsettled and morally complex. The story closes with a chilling final image: the two sisters step into an elevator, the doors slowly closing, and the face of the girl left behind on the other side morphing into Eun-Joo’s, a haunting reminder that past decisions echo into the present in ways that never fully vanish.
