A lonely and shy young woman, inherits a house and stumbles upon a secret formula that enables her to transform her body in any way she wants.

Ellen receives an exotic mask by mistake and begins to have waking nightmares and hallucinations. Her husband and doctors believe she is a paranoid schizophrenic and take her to a psychiatric ward. On the way to the hospital the car breaks down, her husband rushes off to get gas, and the Nightmare Man appears. Ellen escapes and stumbles upon a country house where two young couples are spending the weekend. They do not know if the killer is real or just a figment of Ellen's tortured mind nor if the killer is outside or already inside the house.