Three men seek out the secret of two long-abandoned villages built on opposite sides of a valley; their only clue is the vast array of what were once mirrors, built to face each other across the river. By setting up mirrors of their own, they might learn what happened here...but will they get more than they bargained for?
A trio of travellers led by a man named Okada arrives in a remote valley in the northern part of the "K" River. They find two small villages, Kimon Vale and Kimon Glen, built on either side of the river. Both villages had been deserted many years ago, and they had each placed mirrors everywhere to face into the other village. In the present, all of the mirrors are shattered and ruined; in the rare periods of light during the winter, the valley glitters from all of the glass fragments littering the ground.
As the group examines the villages, they review what little they know. According to legend, a persecuted tribe fled into the mountains, only to fall victim to infighting that split it into two factions. The factions established villages on either side of the river, nursing their bitter enmity for centuries before disappearing without a trace a few decades ago. No one knows what happened to the people, or why there were so many mirrors set up around the area.
As an experiment, the travellers set up mirrors on either side of the river, hoping to find clues about the fate of the two villages. After a few moments, a strange humming begins to echo through the air as the group sees a vision of the past in the mirrors.
Hideo, a man from Kimon Glen, had fallen in love with Toyomi, a woman from Kimon Vale. Their attempts to see each other and elope were constantly stymied by the other villagers, who were appalled at the thought that one of their own would consort with the "enemy". It is revealed that the tribe that founded the villages were exiled because of the "evil eye" in their lineage; by staring with malicious intent, they can inflict physical pain on others. The only defense against this power is to deflect it; the mirrors established on either village are intended to reflect their rival's hatred. The humming in the air is the sound of the villagers' accumulated hatred bouncing back and forth across the river.
Eventually, Hideo and Toyomi committed a lovers' suicide to escape their villages' hatred; their bodies would be found in the middle of the river, holding hands. From then on, their ghosts would appear every night and make love to each other, horrifying everyone in Kimon Vale and Kimon Glen. Inflamed by this display, the hatred between the villages grew exponentially, with people on each side screaming for the other to burn. Finally, when the animosity reached its peak, the ghosts of Hideo and Toyomi shattered like glass, followed by every mirror in both Kimon Vale and Kimon Glen.
In the present day, the travellers recoil in pain as the humming noise intensifies. Okada realizes that they're hearing the sound of the villagers' hate reflecting from the mirrors; their experiment has accidentally awakened the lingering enmity between the old villages. As the humming of hatred becomes unbearable, Okada attempts to terminate the experiment by shattering the nearest mirror with a rock, but he stops short when he sees that his own reflection has gained the "evil eye" of the lost Kimon clan. His colleagues notice the same effect in their own reflections before the mirror shatters on its own; an instant later, the men themselves follow suit.
The final narration notes that the former site of Kimon Vale and Kimon Glen has become known as "the Valley of Mirrors", and no one has ever managed to unravel its mysterious history.