Shamoto runs a small tropical fish shop and leads a boring, but stable life. His second wife, Taeko, does not get along with his daughter, Mitsuko, and this worries him. He also feels somehow unfulfilled and dissatisfied with what his life has become.
One day Mitsuko is caught shoplifting at a department store. There they meet a friendly man named Murata, who helps to settle things between Mitsuko and the store manager. Since Murata also runs a tropical fish shop, Shamoto establishes a bond with him and they become friends; Mitsuko even begins working for Murata and living at his house, to avoid conflicts with her stepmother.
What Shamoto doesn't know, however, is that Murata hides many dark secrets behind his friendly face. He sells cheap fish to his customers for high prices with his artful lies. If anyone detects his fraud or refuses to go along with his money-making schemes, they're murdered and their bodies disposed of by Murata and his wife in grisly ways. Shamoto is slowly taken in by Murata's tactics, and by the time he realizes that Murata is insane, and a serial killer who has made over fifty people disappear, he is powerless to do anything about it. But now Mitsuko is a hostage at Murata's home, and Shamoto himself has become the killer's unwilling accomplice!
Meanwhile, the murders, without any trace of the bodies, continue unabated. The police have long suspected Murata and try to get information about him from Shamoto; Murata quickly senses the danger and threatens Shamoto not to report anything to the police.
In the end, the conflict between Shamoto and Murata will result in murder, insanity, and an ordinary man being driven to the edge of the abyss.