On a deserted island in the sea, two survivors of an airplane crash have been awaiting rescue for three weeks, and are joined by three survivors involved in a boat accident. Pushed to their limit, the group decide to create distance between themselves and share food in order to survive. Until one day, the dead body of Ichinose, one of the survivors is found washed up on the beach.

The year is Genroku, during the reign of Tokugawa Tsunayoshi. In a remote, snowbound village deep in the mountains, a body is discovered. The scene is gruesome—flesh from chest to abdomen has been savagely torn apart, as if by a relentless saw. Someone mutters: "The Saw Demon... It must be the Saw Demon’s doing..." As the cold rain continues to fall, sealing the village from the outside world, hidden motives and quiet fears begin to intertwine.