Promote the development of the plot. It was the death of his wife that made Mr. Lang Dan, whose income was not high, get into trouble soon. It was this dilemma that prompted him to think of selling his wife's "fake jewelry" and unlock the secret of his wife and "fake jewelry". In characterization, it is the advancement of this plot that exposes the true face of Mrs. Langdan and the greedy, selfish and shameless face of Mr. Langdan. Thereby deepening the theme of the novel.