From librivox.org:
One of the first horror novels, it tells the story of Melmoth, who sells his soul so he could have an extended life. Throughout the novel, he wanders around the world in search of someone who would replace him and lift his curse. It is known for its many sub-plots, the true horror it makes one feel, and its criticism of the Catholic church. This is certainly one of the most important books of all times, quoted in countless other works, and praised by authors and critics alike. - Summary by Wikipedia and Stav Nisser.