A woman attacks a priest in a confessional after claiming that the darkness had overtaken her. She fights off several men before collapsing and dying for no apparent reason. Doyle says her strength most likely came from adrenaline and her death was from stress induced ventricular fibrillation. He thinks she was literally scared to death.
The victim, Molly Morgan was just released from a mental hospital, nicknamed Bedlam. She had a weak heart and a history of delusions. She was friends with Simon, who was also released. He’s found catatonic after a priest attempts an exorcism.
Both Molly and Simon have the same pattern of dots on their necks. Doyle thinks it could be a pentagram left by the demon Abadon, which they find in one of Adelaide’s books. Houdini questions why Adelaide even has such a book. Turns out her husband wore a ring with an odd symbol which was used by a violent Polish anarchist group. Adelaide thinks her husband was trying to stop them and they killed him and left him hanging in his study for her to find.
A defrocked priest, Nathaniel, residing at Bedlam, claims that Molly and Simon were his followers. Nathaniel tells Doyle that Doyle’s deepest fear is to be condemned in a place like Bedlam.
Dr. Pilson tries to use the patients fears to make them accept God. Doyle tells Dr. Randall that he plans to investigate Bedlam. The two discuss it over tea. Later Doyle recalls his father being dragged away while telling him to stop whining. Turns out Doyle’s father was institutionalized and Dr. Pilson was his doctor and the files show he tortured him to death. Doyle gets drunk and goes after Dr. Pilsen, who commits him.
Doyle is set up for Nathaniel’s murder in the asylum. Dr. Pilsen uses it as a reason to perform a lobotomy but a man with delusions of being Sherlock Holmes saves him. Unfortunately they end up back in their cell.
It turns out that Doyle isn’t institutionalized at all. It’s all a drug induced nightmare. Suddenly he’s spending time with his wife and she doesn’t want him to go back. His other fear is having to watch her die back in the real world.
Houdini and Adelaide realize that Doyle never made it home and they find him unconscious and dying. Houdini figures out he’s been poisoned but they have to find an antidote. They believe that Dr. Randall poisoned him. When he refuses to hand over the antidote, Houdini poisons his tea. Randall claims he was only trying to cure madness by inducing fear to better understand it and hands over the antidote to save himself.
Houdini rushes to save Doyle before it’s too late but he trips and falls and the vial breaks.
Inside the dream, Doyle figures out that his darkest fears have to do with his father. He talks to his father in the dream, about how he hated him. HIs father explains that he hated his son’s writing because his brilliance made him feel even more of a disappointment. When his father finally hugs him in the dream, the euphoria he feels helps combat the poison and he lives.
Adelaide shares with Houdini that the police believed that her husband lost all of his money gambling but she believes the money was embezzled. She continues to look into her husband’s best friend’s murder, Nigel Pennington. The evidence shows he was strangled. Later that night, Adelaide finds a note on her desk that say, “Drop this or die.”