S4E23 · Demons

Fox Mulder 's (David Duchovny) mind flashes back to being in the attic with his sister Samantha while their parents are arguing downstairs. Back in the present, Mulder wakes up in a hotel room in Providence, Rhode Island, covered in blood. Mulder calls Dana Scully (Gillian Anderson), who arrives, finding him in shock. Mulder has a pounding headache and has no memory of what he has done in the past two days. Scully finds that two bullets have been fired from Mulder's gun and that he has keys belonging to a David and Amy Cassandra.

Scully wants Mulder to check into a hospital, but he wants to find out if he was involved in a crime before doing so. The agents arrive at the Cassandras' house where the housekeeper tells them they are not at home. Mulder recognizes a house in many of the Cassandras' paintings: a house that is near his parents' summer home in Rhode Island. When they arrive there, Mulder has striking pains in his head and flashes back again to when he was a child, seeing a younger version of The Smoking Man (Chris Owens) in his home. The agents enter the home, where they find the Cassandras dead from gunshot wounds.

The agents call the police, who take Mulder with them due to the circumstantial evidence against him. Scully performs an autopsy on Amy Cassandra, finding a scab on her forehead. The detective in charge of the case tells Mulder that they have found David and Amy's blood on his shirt. Mulder refuses to confess to the murders, not remembering anything. Scully arrives, saying she found in Amy's blood traces of ketamine, an anesthesic substance that has hallucinogenic properties. The substance was detected in Mulder's blood as well. Meanwhile, one of the officers at the station kills himself; he has similar symptoms to that of the Cassandras.

Mulder suffers a seizure and flashes back to his childhood again, witnessing his parents arguing with The Smoking Man. Scully sees Mulder the next day, telling him that she believes that the Cassandras killed themselves after receiving psychiatric treatment and that Mulder was visiting them about their alien abduction experiences.

The agents visit Dr. Goldstein in Warwick, Rhode Island, who was treating Amy with an aggressive method to help her recover her abduction memories. Goldstein also treated the police officer, but says he has not met Mulder before. Mulder has another painful flashback of The Smoking Man arguing with his mother, Teena Mulder. Mulder declines Scully's request that he go to the hospital and goes to visit his mother, demanding she explain what really happened when they had to make a choice between him and Samantha. Mulder believes that The Smoking Man forced them to take Samantha.

Mulder also questions who his father really is. Mulder's mother gets upset and refuses to provide him answers. Later Mulder visits Goldstein, and convinces him to again treat him so he will remember what really happened. Mulder has further visions of the past. Scully and the police arrive soon after to arrest Goldstein but find Mulder gone. Scully finds him at the family's summer home in Rhode Island and is able to calm him down. While Mulder is cleared in the deaths of the Cassandras, what truly happened when he was a child remains a mystery.