In 1920s England, a group of friends turns a long drive into a friendly, competitive journey toward Land’s End. Among them is Daphne Welles Hunter and her partner Billy, who end up stranded when their car runs out of petrol. Billy sets off to find a nearby garage, but the search drags on, and Daphne decides to go after him herself. The delay proves deadly; when Billy returns to the car, Daphne has vanished.
Daphne’s search leads her to a secluded mansion, where the owner, Dr. Lawrence, a former clergyman, greets her with a measured hospitality and offers her a place to rest for the night. He sends his servant, Ayah, to summon Tom Rawlings, the caretaker, while Daphne settles in. Tom finds Billy and the other party-goers, the couple Angela and Geoffrey, and informs them that Daphne has disappeared, though the details are hazy.
Lawrence’s memories come into sharper focus through a chilling flashback. He recounts his work as a missionary in India, where a satanic cult supposedly abducted his son, Simon, and twisted him into an evil presence. The tragedy hardens Lawrence’s faith into renunciation, a choice that haunts him as he keeps Daphne sheltered in the mansion for the night. Into this tense tableau, the atmosphere thickens as Ayah quietly releases a deformed man from the attic—the figure who will cross paths with Daphne in her room. The intruder attacks and kills her, then is fed by Ayah to sustain the man’s cannibalistic state.
With Daphne’s fate unresolved, the local police decline to organize a search, citing the treacherous marshes. The remaining friends take matters into their own hands, splitting up to scour the area. Angela finds the mansion again, and Tom pleads with her not to enter, but she presses on. Tom eventually locates Billy and Geoffrey and breaks the grim truth to them: Daphne’s murder was carried out by a cannibal in the attic, a figure tied to Lawrence’s secrets. Desperate and frightened, they go to the mansion, where a noise from the attic confirms their fears.
Geoffrey bravely investigates the attic and is killed by the cannibal. The truth about the killer is revealed: the cannibal is Simon, Lawrence’s son, who has remained in a monster’s grip since his supposed conversion. Ayah is described as a sacrificial cult member whom Lawrence recruited from India to prepare Simon’s meals, a terrible detail that deepens the family’s guilt. Lawrence reveals that he has kept Simon alive as promised to his late wife Harriet, a vow that now weighs on him with crushing sorrow.
Simon escapes his confinement, and Tom, who has slipped into the guest room, confronts Billy and Angela. Simon bursts in and kills Tom, sparing no one in his path as he turns toward Billy and Angela. Lawrence arrives and, reluctantly, shoots Simon dead to protect the others, an act that leaves him shattered. Overcome by despair and remorse, Lawrence takes his own life. Dawn breaks as Ayah steps back, quietly permitting Billy and Angela to flee the mansion and begin the long, uncertain trek toward safety. The shadows loosen with the morning light, but the memory of the night’s dark revelations lingers.
