Sergeant Major Seong-gyu Noh Cheon Ho-jin and a fellow soldier pay their final respects to Noh’s wife, a quiet moment that starkly contrasts with the grim work ahead. In the car after the ceremony, the friend delivers news of an official assignment: Noh is to travel to Guard Post 506 at the Korean DMZ to investigate a disturbingly strange incident. The mission carries more weight than a routine check, because something at 506 has already disrupted the normal rhythms of the post and hinted at dangers beyond a simple accident.
At GP 506, Noh arrives after nightfall, and the atmosphere quickly thickens with unease. On the way to the office, he passes a boiler room defaced with bloody words: “Kill all of them.” The recreation room where bodies were found becomes a grisly tableau that shocks him into a harder focus. He starts pulling at clues, comparing what the records show with what the soldiers around him report. A troubling pattern emerges: weapon handling has changed, with personal arms being kept outside the barracks—an unusual and alarming deviation that signals something more sinister than a mere training mishap.
Soon, a new lead appears in the form of a survivor, a man who claims to be Yoo. In the present timeline, Noh pores over the guard post’s records, looking for connections between the abnormal weapon management and whatever happened in the generator room. A soldier comes forward with the news that another survivor exists, one who was found in the generator room, and this man’s identity becomes a focal point of the investigation. Noh’s instincts tell him that the survivor’s story is not credible, and he resists the orders to bring Yoo back before the investigation is complete. He refuses to let the cleanup crew dictate the tempo of truth and pushes to uncover the deeper layers behind the apparent events.
The diary of Corporal Kang [Lee Young-hoon] provides a crucial thread in the unraveling mystery. As Noh reads, he notices that Kang’s notes describe a mind-breaking confusion among the troops, yet they fail to fit the portrait of a single, clear-cut “insane” killer. The investigation widens as the surgeon on the post, the Doctor [Lee Jeong-heon], returns with bodies that challenge conventional explanations. The situation grows tenser when Cpl. Kang falls into a critical condition, and defibrillation attempts fail to revive him. The room darkens with the fear of an unseen threat, and when Noh glimpses the shape of a dark silhouette in the medic room, it confirms that something beyond human behavior is at work.
A second, more troubling possibility emerges: a disease is spreading through the men of 506. Doctor [Lee Jeong-heon] hypothesizes a rabies-like virus that drives violence and cannibalistic aggression, yet he cannot determine how transmission occurs. What persists, however, is a cruel rhythm: a remission period where rashes disappear and the afflicted seem normal, only to relapse with even more violence. The clock ticks in the bunker as new symptoms appear, and the ratio of infection to survival becomes a brutal calculation. In this tense environment, Noh’s mind starts tracing how the pieces connect—how a single misrepresented report could have cascaded into a disaster of this scale.
A shocking truth surfaces: the medic who claimed to be Yoo was not telling the truth. In a flashback, the medic’s lie is exposed as the real Yoo confronts the consequences of his own choices, revealing a chain of deception that reaches toward Lt. Yoo [Jo Hyun-jae], who actually led the group into the forest and who bears the responsibility for the spread of the disease. The revelation reframes past testimonies and forces Noh to reassess who can be trusted and who must be held accountable for the catastrophe.
As the investigation intensifies, an escalation in violence ripples through the ranks. The group splits into camps, some insisting on stripping weapons from the infected, others arguing that the disease cannot be controlled without drastic measures. Tension peaks when Kwon, a figure tied to the truth of the outbreak, is constrained by bonds and a failing sense of self-preservation. His testimony is a mirror of the post’s harsh realities: HQ did not stand by the troops when they were dying, but instead treated them as expendable assets in a larger cover-up. Kwon’s stubborn insistence on telling a version that saves his life clashes with Noh’s sense of duty, and the two clash in a confrontation that exposes the raw edges of leadership under siege.
The moral dilemma comes to a dramatic head when Noh learns the full scope of the tragedy: the virus is a destroyer that does not respect ranks or loyalties, and the only way to stop it appears to be to kill everyone who is alive within the bunker. Doc [Lee Jeong-heon] objects, arguing that such a act would be genocide, but Noh’s resolve hardens as he discovers that both he and Doc are infected. In a final, desperate act, Noh moves through the bunker, turning the spaces into traps and preparing a last line of defense that would erase the threat by any means necessary.
The standoff with the remaining soldiers—led by Lee and the others—reaches a fever pitch as kerosene is sprayed through the corridors and the bombastic risk of explosion becomes the only option left to stop the disease. The Doctor’s defense collapses as ammo runs out, and Doc is killed in the crossfire, leaving the bunker to be overtaken by a deadly silence that only the smell of petrol and smoke can break. A single Private manages to escape the bunker doors, but a booby trap detonates, and the complex is swallowed by fire and ruin. The clock reads 06:57 as the post crumbles into scorched ruin, the last survivors reduced to memory.
In the final act, the story returns to the taped recording by Corporal Kang [Lee Young-hoon], which explains the virus, the choices that led to the catastrophe, and, chillingly, the method to stop it—by ending the lives of all who remain. The closing image returns to a barrack scene where a cake with burning candles sits atop an innocently celebratory surface, only for the burning candles to hint at the darker finale: the act of killing everyone left alive. The film leaves the audience with a stark meditation on fear, loyalty, and the price of survival under an uncontainable threat, long after the echoes of the explosion have faded.
