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.