After the greedy relatives arrive at the family home, chaos ensues as they are met with resistance from the remaining family members. The children, Virginia (played by Jill Banner) and Elizabeth (played by Beverly Washburn), are particularly disturbed and protective of their home. Their brother, Ralph (played by Sid Haig), who is the most severely affected by the Merrye syndrome, is kept hidden away in the basement.
As the relatives try to navigate the strange and macabre family dynamics, they are met with increasingly violent and disturbing behavior from the children. Virginia and Elizabeth have a penchant for playing deadly games, complete with traps and dangerous pranks. The chauffeur, who cares deeply for the children, tries to maintain some sense of order as things spiral out of control.
The tension escalates as the relatives become more desperate to take control of the family's estate, leading to a climactic and bloody showdown between the two factions. The true extent of the family's madness is revealed in shocking and horrifying ways, leaving the survivors to grapple with the dark legacy of the Merrye syndrome.