The Question and Answer section for The Fall of the House of Usher is a great resource to ask questions, find answers, and discuss the novel.
C. His childhood friend and owner of the house, Roderick Usher, invited him by letter to come visit because he is sick.*
The mood in the first paragraph is dark, dismal, and foreboding.
One example of irony can be found in theb story's title, the fall of the house of Usher decribes both the literal decay of the family home, and the end of the family name (line).