In a land long ravaged by war, Minju grows up hearing tales that on certain nights, the spirits of the dead roam and take the living. After discovering that her guardians plan to sell her as a human sacrifice to a river god, she flees into the mountains. Lost in the darkness, she is saved by a mysterious being known as Baekgwi—a white-haired spirit clad in armor.

Baekgwi offers her a grim bargain: if she can find his missing corpse within ten days, he will spare her life. If she fails, he will kill her. As Minju struggles against time to uncover the truth hidden in the mountain, she begins to question the true nature of Baekgwi—whether he is truly a ghost, and what binds him to the world of the living.