American professor John Holden arrives in London for a conference on parapsychology only to discover that the colleague he was supposed to meet was killed in a freak accident the day before. It turns out that the deceased had been investigating a cult lead by Dr. Julian Karswell. Though a skeptic, Holden is suspicious of the devil-worshiping Karswell. Following a trail of mysterious manuscripts, Holden enters a world that makes him question his faith in science.
Nanny, a London family's live-in maid, brings morbid 10-year-old Joey back from the psychiatric ward he's been in for two years, since the death of his younger sister. Joey refuses to eat any food Nanny's prepared or take a bath with her in the room. He also demands to sleep in a room with a lock. Joey's parents -- workaholic Bill and neurotic Virgie -- are sure Joey is disturbed, but he may have good reason to be terrified of Nanny.
In foggy London Dr Jekyll experiments on newly deceased women determined to discover an elixir for immortal life. Success enables his spectacular transformation into the beautiful but psychotic Sister Hyde who stalks the dark alleys of Whitechapel for young, innocent, female victims, ensuring continuation of the bloodstained research. With each transformation Sister Hyde becomes the more dominant personality, determined to eventually suppress the frail, ineffectual Dr Jekyll forever.
