Members of an Irish family are being killed off by one of their own who wishes to inherit the family fortune.

In Ireland near their family castle John Haloran and his wife, Louise, argue over the will of John's half-crazy mother, Lady Haloran, and in the heat of the discussion, John dies of a heart attack. Louise, whose primary concern is to gain control of the family wealth, conceals his death, fearing that she will be cut off from the inheritance. The Halorans, including Billy, Richard, and Richard's fiancée, Kane, gather for a memorial ceremony at the gravesite of Kathleen, their sister who was drowned in a nearby lake 8 years earlier. Meanwhile, the scheming Louise plots to drive Lady Haloran insane by making her believe that she can communicate with the dead child; before she can carry out her plan, however, Louise is brutally axed to death. Justin Caleb, the sinister family doctor, becomes suspicious of everyone, and after Lady Haloran is found murdered, he orders the lake drained. A wax statue of Kathleen is found; Billy appears, brandishing an axe; but he is overcome and killed. It is revealed that Billy, a homicidal maniac, also was responsible for his sister's death.