Following the trend of adapting horror video games into feature films (like Resident Evil and Silent Hill), director Yukihiko Tsutsumi has taken on the popular Japanese game Sairen (or Forbidden Siren) and turned it into a full-length movie.

Forbidden Siren tells the story of Yuki Amamoto, who goes to live on the solitary island of Yamajima with her father and her sick younger brother. The island has a strange history: In 1976, its entire population was killed except for a crazy man who kept shouting, "When you hear the siren, never go out."

When Yuki arrives, her neighbor issues the same strange warning about staying indoors every time the siren is sounded. One night, Yuki hears the siren wail. However, her father decides to go out to the forest to take pictures of nocturnal animals. When he returns home, he seems not quite himself anymore.

Yuki begins to investigate the mysterious goings-on in the island, and finds out the chilling truth behind the killings in 1976. However, by the time the siren is sounded for the third time, she realises that she is too late...