Opium and absinthe

Are the mysterious murders in New York City the work of a human or a vampire?
Tillie Pembroke's sister is found dead and without a drop of blood. Only two small wounds on her neck indicate where the life escaped from her. It was around this time, in the late 19th century, that Stoker's Dracula was published in America, and so many people's imaginations turned to the possibility that a vampire had gone on the rampage in New York.
Tillie is a voracious and inquisitive reader, so this explanation of her sister's death cannot satisfy her. He won't rest until he gets to the bottom of the mystery. Her search is hampered by a nasty injury she sustained in a fall from a horse. The doctor prescribes laudanum, an opium tincture, to ease her pain, and some people in her neighborhood are suspiciously willing to supply her with the drug.
She tries to apply logic and science to her investigation, even discovering more victims of the strange killer, but the ever-increasing doses of opium cloud her mind. Even for a girl who relies on her own reason, it becomes increasingly difficult to distinguish what is real and what is not, and especially who she can trust among her family.