A demon mother has nine sons, but she eats eight of them without them realizing she is a demon. When it is time for her to eat the ninth son, the son’s wife tells her husband that his mother is a female demon, but he does not believe her words. Later, the ninth son carries out an investigation according to his wife's words, during which he finds out that his mother is really an iron-mouthed demon. At last, with the help of his wife, the ninth son finally escapes from his demon mother.