Dementia 13 - Plot

Plot

One night, while out row boating in the middle of a lake, John Haloran and his young wife Louise argue about his rich mother's will. Louise is upset that everything is currently designated to go to charity in the name of "a mysterious Kathleen." John tells Louise that if he dies before his mother does, she will be entitled to none of the inheritance. He then promptly drops dead from a massive heart attack. Thinking quickly, the scheming Louise throws the fresh corpse over the side of the boat, where he comes to rest at the bottom of the lake. Her plan is to pretend that he is still alive, in order to ingratiate her way back into the will. She types up a letter to Lady Haloran, inviting herself to the family's Irish castle while her husband is "away on business".

Upon arrival, she immediately notices that things are a little strange in the castle. She observes John's two brothers, Billy and Richard taking part in a bizarre ceremony with their mother as part of a yearly ritualistic tribute to their youngest sister, Kathleen, who died many years before in a freak drowning accident. Lady Haloran still mourns for her, and during this year's ceremony, she faints dead away. As Louise helps her into the house, her mother-in-law tells her that she fainted because one of the flowers she had thrown had died as it touched Kathleen's grave.

Louise, realizing that Lady Haloran is emotionally overwrought and superstitious, devises a plan intended to convince the old woman that Kathleen is trying to communicate with her from beyond the grave. This plan involves stealing some of the dead girl's old toys and placing them at the bottom of the estate's pond where they will float to the surface in the middle of the day in an ostensibly ghostly way. At night, Louise swims into the pond and begins placing the toys as planned. However, she is shocked to see what appears to be Kathleen's perfectly preserved corpse at the bottom of the pond. Horrified, she swims to the surface... and is abruptly axed to death by an unknown assailant. The killer then drags Louise's bloody corpse away.

Concerned family doctor Justin Caleb arrives and becomes determined to solve the mystery. He questions the family in an intense, almost insane manner. Meanwhile, the murderer strikes again, decapitating a man who is poaching on the estate. Caleb has the pond drained, revealing a stone shrine for Kathleen, with the words "Forgive Me, Kathleen" on the monument. The following night, Lady Haloran is attacked by a shadowy figure, but she survives.

Finally, Caleb utilizes an obscure nursery rhyme ("Little fishies in a brook, papa's hanged you on a hook") to help him discover Louise's corpse hidden in a meat freezer. Next to the body is a wax figure of Kathleen. Caleb places the figure in a public square to lure the killer. Taking the bait, a gibbering Billy attempts to kill Richard's fiancée Kane with an axe; he has become insane with the guilt he has felt for years over having caused the death of his sister Kathleen. Caleb removes a gun from his coat pocket and shoots Billy to death.