Kaoru and her brother Tsuyoshi are driving to a distant town to visit their friend Izumi. When they arrive, they accidentally run over a woman. They attempt to take her to a hospital, but all the roads are blocked by gravestones, which are erected in the middle of the road. She dies and they hide her body inside the car before going to meet Izumi.
When asked about the gravestones, Izumi explains that they lie at the exact spot where someone died; all the houses have gravestones in them and the roads are full. The graves are there because people who die in town physically turn into gravestones upon death. However, if someone touches the corpse, the process will be interrupted and the person is trapped in a state of metamorphosis. If this happens, they must be thrown into a bottomless well that was dug for such a situation.
After Izumi's sister doesn't return home, Kaoru and Tsuyoshi realize that she is the woman they accidentally killed. Her corpse has turned into a pile of ossified remains because she cannot transform into a grave. Kaoru and Tsuyoshi decide to leave town that night. They stop by the well to throw the body into it. Tsuyoshi cuts his hand while dragging the body and later hallucinates that the remains of the people who could not transform rise out of the well and attack them.
Kaoru and Tsuyoshi go home, ridden with guilt. Izumi's letters tell them that her father has become very ill with depression. Tsuyoshi soon dies from an infection in his injured hand. He, too, is stuck in a state of metamorphosis and his remains burst from his grave. Kaoru decides the only thing she can do is to hand herself over to the police. She first goes to Izumi's house to tell the truth, but no one is there. Instead, she finds three fresh gravestones behind suicide notes and empty bottles of pills.