In nineteenth century middle-Europe, orphaned teenage twins Maria and Frieda go to live with their uncle Gustav Weil, who heads the Brotherhood, a vigilante group trying to stamp out vampirism. But their methods are random and misplaced and the only result is a terrorised populace. The real threat lies with Count Karnstein, and although the twins seem outwardly to be identical, Frieda finds herself much more drawn than her sister to the Count's castle dominating the skyline.