Plot
Soo-hyuk, an elementary school teacher in a rural village, has a secret. Every night, his wife Yi-young turns into another person.
One day the father of one of his students comes to know of their secret. Soo-hyuk begs him not to tell anyone, but the father informs the village that Yi-young's body is possessed by a spirit each night. The townspeople conclude that Yi-young is dangerous, and install a cage in her home. They agree that every night, Yi-young is to enter the locked cage, and the student's father will take possession of the key. When the sun rises each morning, the father will return the key to Soo-hyuk. Unable to bear the thought of leaving his wife alone, Soo-hyuk too goes into the cage with her.
That night, a terrible misfortune is visited upon the dark house. A fire starts inside the cage, and Soo-hyuk and Yi-young burn to death. The formerly quiet village is turned upside down by this fire incident.
Before long, a police detective named Hyung-gu comes to investigate the fire. One by one, he begins to interrogate the townspeople, and an uneasy atmosphere settles over the village. One night the villagers invite the outsider Hyung-gu to the Town Hall for a drink. The oldest man in the village tells Hyung-gu that everything is his fault, and fills the detective's glass with mushroom liquor. After drinking, Hyung-gu loses consciousness.
The next day, Hyung-gu wakes up in the cage as it was before the fire. But everyone refers to him as "Teacher". He realizes he'
