In
modern-day Seoul, an ominous wave of unexplained phenomena, ritualistic murders,
possessions, and mass hysteria grips the city. The source of the chaos is a shadowy cult known as the Black Mass, a secretive organization devoted to summoning an ancient demon named
Asmodeus. As their dark rituals gain momentum, the city's regular law enforcement finds itself helpless in the face of such supernatural terror. Desperate for a solution, they turn to a mysterious trio known only as the "Holy Night." The Holy Night is a demon-hunting unit made up of three unique individuals. Ba Woo, a gruff and powerful fighter with
superhuman strength, leads the group. Haunted by a tragic mission in his past, he is driven by an unrelenting sense of justice. Sharon, a serene yet fierce
exorcist, is the spiritual core of the team. Gifted with the ability to sense and expel evil spirits, she draws her power from ancient rites and deep personal faith. The third member, Kim Gun, is a young tech genius and documentarian who brings knowledge, research, and strategy to the table. Though he lacks supernatural powers, his quick thinking and resourcefulness make him indispensable. When the young girl Eun-seo begins exhibiting terrifying signs of possession, her older sister Jung-won, a rational and skeptical
neuropsychiatrist, seeks out the Holy Night team.
Traditional medicine has failed, and Jung-won, desperate to save her sister, is forced to confront her disbelief in the paranormal. The team discovers that Eun-seo is being groomed by the Black Mass cult to serve as the vessel for Asmodeus during a catastrophic summoning ritual. As the Holy Night
investigates, they uncover a disturbing pattern of disappearances,
desecrated churches, and hidden ritual sites scattered throughout Seoul. They face violent confrontations with possessed cult followers, survive visions meant to shatter their sanity, and endure attacks designed to tear them apart emotionally and physically. Ba Woo struggles with nightmares of the past, Sharon faces moments of wavering faith, and Kim Gun uncovers that his own estranged father was once involved with the cult's earlier
incarnation. Time runs out as the cult prepares for the final ritual in a decaying cathedral hidden beneath the city. The Holy Night storms the site in a desperate bid to stop the
summoning. A violent and emotional battle breaks out. Ba Woo takes on the cult's possessed enforcers, Sharon engages the high priest in a spiritual battle of incantations and
willpower, and Kim Gun disables the protective spells that shield the ritual. Eun-seo, fully possessed by Asmodeus, threatens to unleash unimaginable destruction. In a bold act of self-sacrifice, Ba Woo allows the demon's essence to partially possess him, using his body as a temporary vessel. With Sharon guiding him through a final exorcism rite, Ba Woo uses the demon's own power to destroy the summoning circle. The backlash of energy nearly kills them all, but it successfully banishes Asmodeus back to the
underworld and frees Eun-seo. After the battle, the cult is broken, but scars remain. Eun-seo begins a slow recovery, her memories fragmented. Jung-won, now a believer, chooses to assist the Holy Night in future missions using her medical expertise. The trio, though battered, survives aware that evil never fully dies. In the final scene, the Holy Night receives another mysterious file proof that new darkness is already brewing elsewhere. ==Cast==