The HORROR OF DRACULA (1958) was a cult classic film that every  writer of horror should check out! The screenplay is by Jimmy Sangster, one of the producers and writers of the legendary Hammer Studios.

IMDB: Jonathan Harker takes employment with Count Dracula, ostensibly to catalog his vast library. In fact, he is on a mission to kill the Count, a vampire. Before he can do so however, the Count gains the upper hand and Harker soon finds himself as one of the walking dead. Dracula has taken an interest in Harker's fiancée, Lucy Holmwood and it is left to Harker's colleague, Dr. Van Helsing to protect her. He has difficulty convincing Lucy's brother, Arthur Holmwood, of the dangers or even the existence of vampires. Soon, however, Arthur's wife Mina is targeted by Count Dracula and he and Van Helsing race to find his lair before she is lost to them forever.