In this darkly comedic thriller, a mistaken exotic mask sets off a chain of terrifying events for Ellen, who begins to experience waking nightmares and hallucinations that her husband and doctors attribute to paranoid schizophrenia. As she escapes from an attack by the mysterious "Nightmare Man," Ellen stumbles upon a country house where two young couples are spending the weekend - but can anyone trust their hosts? The line between reality and nightmare becomes increasingly blurred, leading to a shocking revelation about the true nature of the Nightmare Man, who is revealed to be a demonic entity that possesses its victims.