Michelle Charter works as a nurse at the Excelsis Dei Convalescent Home. While making her rounds one night, she is suddenly and violently attacked by an invisible entity that proceeds to rape her. News of the attack reaches FBI headquarters, arousing Mulder and Scully's interest in the case. They travel to Worcester, Massachusetts, the town where Michelle works. During her interview, Michelle insists that the spirit which entered her body emanated from an elderly patient afflicted with Alzheimer's disease named Hal Arden. Outraged by the incident, she initiates a lawsuit against the federal government claiming that she is regularly subjected to sexual harassment and has no recourse for protection.

The agents speak with Hal, who assures them he is not strong enough, nor possesses the sexual drive, to rape anyone. Shortly thereafter, Hal begins choking after he secretly ingests a mysterious pill given to him by his roommate Stan. Mulder and Scully are unable to save Hal, and he dies. Dr. John Grago is upset when he learns the news; Hal's Alzheimer's disease had been in remission since he began taking an experimental drug called Depranil. Laura Kelly, Stan's daughter, has her father discharged from the facility because of his markedly improved mental and physical state. She notes, however, that Stan has begged her not to take him away from the home.

The mystery deepens when Tiernan, a hospital orderly, is pushed out a window by an invisible force. A toxicological report on Hal's blood reveals trace levels of Ibotenic acid, an hallucinogenic drug. While searching the basement of the nursing home, Mulder uncovers a room containing hundreds of mushrooms. Beneath a pile of fertilizer Mulder discovers the dead body of a missing orderly. Gung, an Asian orderly, is questioned about the room.

He admits that he has been feeding herbs to the residents that allow them to speak to the dead. Gung is convinced that the mysterious rapes and murders were committed by angry spirits. Stan overdoses on the herbs and a group of ghosts mass for an attack against residents and visitors alike. Michelle and Mulder become trapped inside a bathroom that floods with water. Scully comes to their aid. Grego finds Stan and drugs him. Suddenly, the attacks end and the ghosts disappear. The door to the bathroom suddenly bursts open, sending Mulder and Michelle sliding to the floor in a great rush of water.