Struggling writer Yun-hee finds herself drawn to a local Vietnamese folklore about a girl named “Mười” and her haunted portrait, and she travels to Vietnam after being invited by her old friend, So-yeon. The two friends share a quick chat with Seong-eun and Ji-hoon, during which Yun-hee mentions her semi-autobiographical novel, "Secrets & Lies," which painted [So-yeon] in a negative light. Yun-hee convinces herself that [So-yeon] hasn’t read the book, which was published after she left Korea.
Upon arrival, [So-yeon] warmly welcomes Yun-hee and offers her a spot to stay in a sprawling mansion. Yet the reunion is tinged with guarded questions: So-yeon asks about mutual friends, and Yun-hee fabricates that she has lost touch with them. The surface cordiality masks a deeper undercurrent of unresolved tensions.
The next day, a boat slips them toward an old, abandoned house where the legend deepens. The tale centers on Muoi, a young girl who loved a painter named Nguyen. Jealous and possessive, Hong, the painter’s wealthy fiancée, hires thugs to cripple Muoi and personally disfigures her face with acid. Unable to cope with the tragedy, Muoi takes her own life, becoming a vengeful spirit trapped in the same forsaken residence.
Seeking context, the pair visits the office of a professor, [Kim], who has studied Vietnamese folklore and introduced So-yeon to the legend. Yun-hee swindles past the assistant Eun-jung and steals a notebook containing Kim’s research, hoping to unlock the legend’s secrets. As Yun-hee digs deeper, the world around her grows increasingly unstable: eerie noises, fluttering shadows, prophetic nightmares that replay Muoi’s torments, and the sense that the barrier between their world and Muoi’s is fraying.
Cracks widen between Yun-hee and So-yeon. Yun-hee’s deception comes to light—she has kept in contact with Ji-hoon despite So-yeon’s warnings—and old resentments rise to the surface. A night of heavy drinking drives a painful scene where Yun-hee lashes out and calls So-yeon a slut for dancing with others. The next morning, So-yeon pretends nothing happened, but the rift remains.
A further revelation emerges when [Eun-jung] reveals that So-yeon, not the professor, introduced Kim to Muoi’s legend. Yun-hee then uncovers a connection between a cursed portrait and Muoi, watching a victim describe the same symptoms she herself endures, including Muoi’s reflection appearing in mirrors.
Against So-yeon’s cautions, Yun-hee sneaks into the painting studio and discovers So-yeon’s self-portrait in Muoi’s style, alongside a copy of "Secrets & Lies" with highlighted passages about Yun-hee. Confrontations follow: Yun-hee accuses So-yeon of cursing her, but So-yeon neither denies nor fully agrees, instead offering a cold wish for Yun-hee’s safe journey home.
As Yun-hee begins packing, So-yeon reveals a painful motive rooted in the past: three years earlier, [Ji-hoon] and his friends assaulted So-yeon, and Seong-eun recorded the incident on camera. Rumors about So-yeon’s promiscuity spread, and Yun-hee’s book seemed to amplify those rumors. So-yeon forgives Yun-hee and urges her to visit a temple to learn more about the curse. Yet darkness follows: Yun-hee’s body contorts with agony, and she is unable to cry out for help.
The journey to the temple uncovers a crucial truth about Muoi’s portrait. The portrait, painted by [Nguyen] with monks’ collaboration to trap Muoi, had once been sealed away there. During World War II, a Japanese major named Yoshimoto raided the temple and broke the seal, releasing the curse. The elder monk hands Yun-hee a metal hairpin used to seal the spirit and instructs her to stab the possessed So-yeon to end the curse.
Tragedy strikes when [Eun-jung] is killed in a bizarre accident, and Yun-hee returns to the mansion bearing the hairpin. A secret passage reveals [Kim]’s body, and a photo of Major Yoshimoto—with the caption “Death begins the curse”—tells a darker story. Venturing further, Yun-hee finds a tape recorder with Kim’s recordings, exposing that the mansion actually belongs to Major Yoshimoto and has housed Muoi’s portrait all along.
In the climactic chamber, Muoi’s monstrous spirit finally materializes. A desperate chase ends with Yun-hee stabbing [So-yeon] with the hairpin, and So-yeon delivers a cruel laugh, predicting that her death will herald the curse’s true awakening. A pair of unseen hands grip Yun-hee’s neck as So-yeon dies. Back at the temple, So-yeon’s self-portrait reappears in the spot reserved for Muoi’s portrait, sealing a chilling new twist.
The truth unfolds: So-yeon was the mastermind, orchestrating the entire scheme to take revenge on those who ruined her life. Back in Korea, the now-possessed [Yun-hee] stalks and brutally murders So-yeon’s former friends. She eliminates Seong-eun and [Ji-hoon], burns Major Yoshimoto’s photo, dons Muoi’s ring, and lets a malevolent smile spread across her face as the curse continues to spread its reach.
