In the story "The Fall of the House of Usher" by Edgar Allan Poe, the tone changes from one of melancholy and foreboding to one of horror and terror by the end of the story. The initial tone is set by the description of the decaying mansion and the sickly appearance of the Usher siblings. As the story progresses, the tone becomes increasingly ominous as the narrator witnesses strange occurrences and the mental and physical deterioration of Roderick Usher. By the end of the story, the tone shifts to one of horror as the truth about the Usher family is revealed and the house collapses, symbolizing the fall of the family.