Haiyama, a local official, breaks into a church and releases an unspecified entity that had been imprisoned in the basement. He claims to be the reincarnation of an ancient sorcerer, Dorman. He wants to become village chief and plans to put a curse on his rival.
Two months later, Japan is experiencing a wave of baby abductions, with hundreds of infants kidnapped every day. Kyoichi receives a letter from his parents that his father has given up the family farm to work in a factory that has just opened in their village. Kyoichi is concerned that they would do such a thing without consulting him. He isn't able to call them on the phone so plans a trip to visit them but, as he is going to sleep, thinks he can see his mother watching him at the window.
On the bus back to the village, Kyoichi meets Shoko, an old classmate. She is returning to the village because her father, Haiyama's political rival, has mysteriously become ill. Haiyama is the new village chief and wants to revitalize the area with a newly-built factory and support from the villagers. Kyoichi thinks Haiyama is creepy, and remembers he used to say he was the reincarnation of a sorcerer. Kyoichi observes that everyone in the village is behaving oddly, from his mother to his childhood friend Yukari, who ignores him when he knocks on her window. She is also reading books about the occult.
Kyoichi meets up with Shoko, who agrees that everyone is behaving strangely. Her father is completely bedridden, yet the doctor says it's just fatigue. She has been sent to check on the local priest, whom no one has seen for two months; but they find the church has been burnt down. Yukari appears and Kyoichi discovers that she had deliberately deafened herself by poking a stick into her ear, so that she could not hear the sirens that sound every night at sunset. When Yukari remembers that it is getting dark, she runs away in terror.
Kyoichi sees a giant flying creature in the sky overhead, and he and Shoko chase after it. It leads them to a mysterious tall tower with sirens on top. Kyoichi believes the creaure is a devil, and had seen something similar in one of Yukari's books.
Later, Shoko's father asks her to leave town. A local legend has it that a sorcerer once brought three demons to wreak havoc on the town, two of which were driven away, the third locked in the church basement. He believes Haiyama opened the seal and unleashed the demon. He explains that the factory sirens are mind-controlling everyone, and urges Shoko to cover her ears before they start.
Kyoichi watches as the sirens lure everyone to Haiyama, now addressed as Lord Dorman. He has had the villagers dig an enormous pit for the purposes of a ritual to summon his "Dark Lord." He also sacrifices babies that the villagers kidnap for him. For the ritual to take place the following day, he will need a young woman to sacrifice; and chooses Shoko. Kyoichi goes to warn Shoko, but they are both partially affected by the sirens - they find it difficult to move, and can't bring themselves to leave the village. Shoko's father has died in the night.
Kyoichi ties up his mother to prevent her from going to Dorman. She has no memory of the previous night or of sacrificing babies, but as the sirens sound, she grows wings that were given to her by the demon: Kryffith. The sirens are its voice amplified to the village. She says that most of the villagers, including Kyoichi's father, have been eaten by the demon, and blames Kyoichi and Shoko for what's happening because they moved out of the village.
Kyoichi and Shoko are compelled to attend the ritual. Since Shoko couldn't be found, Dorman has chosen Yukari as the sacrifice. The Dark Lord is resurrected but, instead of Yukari, grabs Dorman and drags him into the pit. Suddenly, all the women present sprout wings and fangs, and devour the men. Shoko transforms into a demon too but Yukari draws a protective magic circle and drags Kyoichi into it with her. Shoko is eaten by the Dark Lord, and all the demons fly off into the sky, where they will soon arrive in the city and the sirens will broadcast their voices to the world.