In a seemingly idyllic London setting, a young schoolteacher named Diana experiences disturbing nightmares as she prepares for her upcoming wedding to an aristocratic war hero. Her fiancé's imposing family home, chosen for the ceremony, triggers haunting visions and eerie occurrences. Struggling with growing anxiety and increasingly violent dreams, Diana begins to question her sanity. As she delves deeper into the house’s sinister past, she meets an American woman named Jenny who is searching for clues about her own mysterious heritage. The two form an uneasy alliance, sharing unsettling experiences that suggest their fates may be intertwined.

Together, Diana and Jenny uncover dark secrets hidden within the house, which seems to amplify their fears and manifest their deepest traumas. Each night, Diana's dreams grow more intense, blurring the lines between reality and nightmare. The malevolent force at play starts targeting both women, pushing them to uncover the truth about their connection to the house and its ghastly history. As danger mounts and paranoia builds, they find themselves trapped in a terrifying web where facing their own demons becomes a matter of survival.