From the back cover:
Terror Crosses the Mists… to Earth The Mists of Ravenloft cannot contain all its terrors. A terrible force invades Earth, weaving a plan that comes together in the 1890s. Only a few intrepid souls risk their lives to prevent the conquest of darkness.
The Red Death Awaits… This campaign setting presents a new look at the popular Masque of the Red Death expansion for Ravenloft, describing an alternate Earth in the 1890s, filled with wonderous inventions, dynamic energy — and untold terror! Featuring new prestige classes, revised magic rules, lairs of evil, and numerous adventure hooks, it provides a wealth of information for players and DMs wishing to explore Ravenloft in a new time and place. Ravenloft books are published under license with Wizards of the Coast and are 100% compatible with v3.5 rules and the d20 System.