The First Layer: The Grandfather's Ghost
The film opens with the Park family plagued by 'Grave's Call'. Sang-deok, Hwa-rim, Bong-gil, and Yeong-geun exhume the grave of the family patriarch. During the process, a greedy gravedigger secretly opens a side pocket and kills a human-headed snake (Nure-onna), triggering a sudden rainstorm that prevents immediate cremation. The coffin is moved to a local hospital mortarium, where an irresponsible worker opens it, releasing the vengeful ghost of Grandfather Park. The spirit slays his son Park Ji-yong by snapping his neck and attempts to kill his newborn great-grandson before Hwa-rim and the team manage to cremate the coffin just in time, lifting the ancestral curse.
The Second Layer: The Vertical Coffin
When returning to the cursed burial site to compensate a laborer, Sang-deok discovers another casket buried vertically directly beneath the original grave. This second coffin is colossal, chained, and wrapped in barbed wire. The team moves it to a nearby Buddhist temple overnight. Unbeknownst to them, the tomb contains a historic Japanese General (Daimyo) who slaughtered thousands during the 16th-century Imjin War. Imperial monk Gisune had surgically placed a cursed samurai sword inside the General's torso and sewn him shut, turning his body into a living, physical 'iron stake' driven into the earth near the 38th parallel.
The Final Confrontation & Cosmic Logic
The Samurai Daimyo awakens as an invincible demonic entity (Oni). It brutally attacks the group, severely injuring Bong-gil and impaling Sang-deok. Realizing that the creature is the iron stake severing Korea’s spine, Sang-deok refuses to flee. During the final battle at the grave plot, Sang-deok remembers the principles of Five Elements cosmology (Wu Xing): the Daimyo monster is composed of Fire and Metal (a flaming sword embedded inside an armored warrior). Brute physical weapons fail because metal cannot destroy metal. According to the cycle of destruction, Water overcomes Fire, and Wood overcomes Metal. Sang-deok drenches a wooden pole in his own blood and water. Holding the blood-soaked, wet wooden club, he strikes the Samurai demon. The wet wood absorbs the fire and shatters the metal blade inside the entity's core, causing the demonic monster to crumble into ash and destroying the iron stake forever.
Ending Meaning
Months later, the team members attempt to return to normal life, attending Sang-deok’s daughter's wedding. However, all four bear lingering physical and psychological scars. The ending conveys that while historical evil can be defeated through unity and sacrifice, the trauma left behind requires long-term healing.