Disclosure: I acquired a free Kindle edition of this public domain work.
Although a bit dry at times, Edith Birkhead's 1921 study of gothic fiction is still a valuable resource for anyone wishing to understand the evolution of the genre. Her insights remain relevant even a century (almost) later.
She starts with Horace Walpole's The Castle of Otranto and moves forward into the novels of Mrs. Radcliffe, Matthew "Monk" Lewis, and others at the end of the eighteenth century. The connections she makes between the authors and the books they read as well as the books they wrote was interesting. Too often, literary analysts seem to assume the books write themselves and evolve one after the other without human intervention.
Many of the books and authors cited have of course been classics for a very long time, but others are less well known and less available even in this age of digitization. It's going to be fun tracking down some of these unfamiliar titles.
One aspect I found particularly interesting, and again given that this was written nearly a hundred years ago, was that Ms. Birkhead recognized the integration of aspects of the gothic story into other genres of fiction, whether bringing elements of the supernatural into the mundane setting such as The Picture of Dorian Grey, or allowing natural fear and terror to heighten the reader's excitement and interest, as in The Prisoner of Zenda.
The edition I obtained is complete with footnotes and index, which will be very useful.