The Guard Post

Sergeant Major Seong-gyu Noh and a friend attend the last rites for Noh's wife, a personal loss that frames his sense of duty. He is then ordered to head to Guard Post 506 in the Korean DMZ to investigate a strange incident. The opening establishes his grief as a catalyst for the crises to come.

At 21:07, Noh arrives at GP 506, about an hour after leaving. He passes a boiler room covered in blood and the words 'Kill all of them' written in blood. He is brought to the recreation room, where the room is covered in blood and bodies.

Back in the present, Noh checks the post's records and notices that weapons have been tampered with, with all personal weapons moved to the armory. A survivor is found in the generator room who claims the name Yoo. The discovery deepens the mystery surrounding the outbreak.

Noh phones his superior, who orders him to bring Yoo back. He refuses, arguing the investigation isn't finished and that a cleanup crew will arrive in the morning. He continues searching for Yoo, checking the canteen but finding nothing.

Noh studies Kang's personal records and notes that he was labeled a troublemaker, yet Yoo's journal hints there is more to the story. He pores over the journal, seeking hidden truths about the outbreak and the lies surrounding it.

Doc returns with the bodies as Cpl. Kang falls into critical condition; defibrillation fails to save him. Kim glimpses a dark silhouette resembling Sergeant Ma near the medic room, which leads to accusations against Yoo and the confiscation of ammunition.

Cold medicine cannot be found in the post first aid room. Kwak and a buddy are sent on sentry duty as men begin to display a red rash, signaling the start of a troubling illness. The situation tightens as supplies run low.

Within hours the disease spreads through the unit as a rabies-like virus that makes men violent. There are remission periods where rashes disappear and consciousness returns, only to relapse into aggression later, making the threat unpredictable.

As Noh continues the investigation, he discovers the soldier they interviewed is actually a medic, not Lieutenant Yoo. The revelation adds layers of confusion and mistrust to the case.

In a flashback, the medic’s deceit is exposed: Kim was killed by Lieutenant Yoo, not Sergeant Ma. Yoo had gone into the forest with the others, and he manipulated the medic to rewrite the report to mislead higher officials.

Kwon leaves the ambulance and is spotted, killing a soldier who has turned into a zombie. He attempts to escape the post, crashes at barriers after Noh opens fire on the ambulance, and is eventually recaptured.

Noh, Doc, 1st Lt. Bang, and the sergeants gather the remaining men for an inspection and sort them by rash status. When the infected refuse to strip their weapons, a tense stand-off ensues and suspicion runs high.

After learning the full extent of the deception, Noh resolves to kill everyone alive—including himself—to stop the virus. Doc objects, but then reveals he is infected, and Noh discovers that he is infected as well.

Noh drenches the bunker in kerosene and triggers a booby trap, turning GP 506 into a burning ruin. He fights the remaining soldiers, and Doc interferes the standoff before being shot by Lee; the confrontation leaves the bunker in chaos.

The film closes with Corporal Kang’s final recording explaining the virus and a grim plan: to kill everyone alive in 506. A scene in the barracks shows a cake with candles before the inevitable shooting to wipe out everyone, underscoring the horror of the outbreak.