The Mysteries of Udolpho

After the deaths of her loving mother and father, a young 18th century French woman of fine character, intelligence, and sensibility is removed from the company of the young man she has come to love when she becomes the ward of her foolish, vain and materialistic aunt; who brings them both suffering and misery when she marries an Italian count who reveals himself as a treacherous schemer, and brings them to live in the decrepit, desolate, gloomy, remote Castle of Udolpho where he works his unsavory plans.

The first full-blown Gothic romance, this novel made Radcliffe the most popular novelist in England in her day. Generally felt to be a bit more clumsy than her much darker novel, The Italian.
Jonkers Rare Books: "The author's fourth book and generally regarded as the seminal Gothic novel. Although preceded and influenced by Walpole's The Castle of Otranto and Leyland's Longsword, The Mysteries of Udolpho contributed most significantly in establishing the Gothic genre."