Detective Shiroshi and his pet assistant Seiji venture to Okuhida to investigate a baffling old case involving people being attacked in the streets. At their ryokan in the mountains, which burn with all the colors of fall, the pair are greeted by a serpent writhing in darkness and the corpse of the landlady, who died suddenly the previous night. Time passes, and another mysterious death occurs alluding to the so-called "serpent's curse." Yet Shiroshi seems to know the true culprit behind the murders, as well as their tragic motives...