 After enlisting as a volunteer in a war in 14th century Japan, his wife and mother remain living in a swamp. They eke out their living by ambushing worn-out warriors, killing them and selling their belongings to a greedy merchant. The woman comes to mistrust her daughter-in-law who has coupled up with a deserter, and begins to wear a facial mask she has taken from a slain samurai. Soon the mask will not come off again. In this disguise she is at first taken for a demon by her daughter.