At the eerie and dilapidated Merrye House, a story unfolds around the Merrye children — Peter Stickles, Brinke Stevens, and Beverly Washburn — who have lived in seclusion with their family chauffeur, Bruno, ever since their parents passed away. These children suffer from a rare and inherited condition known as Merrye Syndrome, which causes them to regress mentally and physically into earlier stages of evolution starting in late childhood. Their condition manifests as a curious mix of playful innocence and feral madness, making them both charming and dangerous.
The eldest, Ralph, is a naïve yet sexually forward simpleton who moves around the house through a dumb-waiter, often unaware of the chaos he fuels. Virginia, obsessed with spiders, is particularly dangerous; she has a disturbing habit of murdering visitors by trapping them with rigged windows and then attacking them with butcher knives, reveling in her savage power. Elizabeth, considered the most responsible among the children by Bruno, is yet also deeply manipulative and obsessed with hatred, embodying a dark side that contrasts sharply with her attempts to maintain control. Despite their violent tendencies, the children harbor a strong affection and respect for Bruno, although they increasingly ignore his warnings against their darker impulses.
The story intensifies when a family of distant relatives arrives — Peter Howe and his sister, Emily, accompanied by their lawyer, Schlocker, and his secretary, Ann. They come to claim the Merrye estate, believing they are the rightful heirs. The house is surrounded by superstition and fear among local townspeople, who deem the mansion cursed. Bruno, desperate to protect the children, hastily teaches them some social manners to present a semblance of civility during the impending visit.
However, tensions rise when Schlocker discovers disturbing secrets in the house’s basement — the sibling of the Merrye family, kept confined in a pit, which shocks everyone. In a brutal turn, Virginia and Elizabeth murder Schlocker to keep their grisly discovery hidden, revealing the true extent of their dangerous nature. Bruno, realizing the gravity of the situation, leaves to obtain dynamite to blow up the house and kill the children rather than see them confined or harmed.
While he is gone, Emily stumbles upon Schlocker’s body and is soon pursued by Virginia and Elizabeth — who attempt to eliminate her as well. Emily, overwhelmed and traumatized, later awakens in the woods, her mind twisted by violence and trauma. Driven by her disturbed state, she returns to the house and savagely attacks Ralph, who is fiercely protected by his sisters. Meanwhile, Peter manages to escape his restraints and helps Ann get free as well.
Bruno reappears with the dynamite and urges Peter to escape, which he does with Ann. In a final act of desperation, Bruno sets off the dynamite, destroying the house and killing both himself and the entire Merrye family amidst the explosion. The survivors reflect on the tragic events, with Peter inheriting the vast Merrye family fortune. He marries Ann and goes on to write about the bizarre phenomenon of Merrye Syndrome, noting that his branch of the family, being distant, was unaffected.
However, the story doesn't end there. Ten years later, while wandering outside, Peter and Ann’s young daughter shows an innocent fascination with a spider, hinting that the dark legacy of the Merrye family may still linger, and the primal instincts awakened in those strange creatures could yet return.
> "They're not really human anymore."
