Bava is credited as writing the film's script along with Alberto Bevilacqua and Marcello Fondato. The film's opening credits credit the stories as "The Drop of Water" by Ivan Chekov, "The Telephone" by F.G. Snyder and "Sem'ya vurdalaka" by Aleksei Tolstoy. Bava later took credit for the original story of "The Drop of Water", but Italian critic Antonio Bruscini traced its origins to a story titled ""Dalle tre alle tre e mezzo"" ("Between Three and Three-thirty") that was included in a 1960 anthology book titled "Storie di fantasmi" ("Ghost Stories"). British historian Julian Granger identified the author of the story as Franco Lucentini. "The Wurdulak" is loosely based on "The Family of the Vourdalak" by Aleksey Konstantinovich Tolstoy The story of "The Wurdulak" was found in the 1960 anthology "I vampiri tra noi". Other parts of the story were inspired by the Guy de Maupassant story "Fear" and Bram Stoker's "Dracula".