After suffering memory loss, Mulder finds out he was part of an experiment of a psychologist involving brain stimulation and surgery. The procedure is experimental and extreme and can lead to suicidal tendencies. Mulder barely escapes from being convicted for the murder of another person taking part in the experiment and her husband. Mulder continues the treatment because it makes him remember what he thinks are details around Samantha's abduction. Scully successfully puts the experiment to an end when Mulder's behaviour becomes dangerous.
A special episode because it's written by XF director RW Goodwin, 4X23: Demons is perfectly in line with the rest of the mythology, past and future -- and it continues to tease us with pieces of information around Samantha, and information that once again may or may not be true.
The experimental method
Dr. Goldstein's unconventional experiment was "an aggressive method to access buried or repressed memories", "a method of therapy that simulates an electrical impulse in the brain, using light and sound". The patient wears a visor that projects flashes of red and blue (the 'memories' are thus tainted) and puts on earphones. Then he is injected in the right hip a "rapid-acting anesthetic", ketamine. It's "a veterinary drug" "but when ingested by a person, it can cause hallucinations". It was first used on american soldiers in the Vietnam War but came to be avoided because it causes out-of-body-like experiences; it continues to be used as a drug ('Special K').
Amy Cassandra, believing she was an alien abductee, contacted Dr. Goldstein in order to remember the time she lost during her abductions. Police officer Fazekas thought he was an alien abductee also (he even read the 'Abductee' magazine issue featuring Amy). Mulder was in the search for a way to remember exactly what had happened to Samantha that fateful night. The treatment had many side effects, among which repetitive behavior that could reach compulsive mania: for Amy Cassandra it was the numerous paintings of her cottage, for the police officer it was cutting out his own picture from his family albums. Then there are the seizures and blackouts, and ultimately depression followed by suicide.
Apparently Mulder contacted Amy because she was an alien abductee, she was the one who told Mulder of this treatment ("I have been here before. I met Dr. Goldstein with Amy Cassandra"). Mulder and Amy kept contact, until one day Mulder was at their home. But even after the episode it is still unclear what really happened with David & Amy. Mulder was there when his gun was discharged but all he remembers is waking up far from the cottage, in a motel. The death of David & Amy must have been a "murder-suicide" as a result of Amy's treatment: Amy in a moment of seizure took Mulder's gun and killed David before killing herself. We don't know why Mulder did not prevent it -- perhaps he was seizuring at that time -- and how he managed, if he was seizuring, to reach a motel.
Were these memories true? Scully does not think so, attributing them to the "Waxman-Geschwind syndrome, the symptoms of which are trance-like states, leading to vivid dreams about the past, dreams that are more detailed than the conscious mind can recall": a construct of Mulder's unconscious, representing exactly what Mulder wants to be true -- for the Cigarette-Smoking Man to be guilty of everything -- but not necessarily genuine. Even so, what we see in Mulder's 'memories' can be coherently tied up with the mythology of the X-Files, and especially in light of later episodes.
Why was the CSM there? After the hints in 3X24: Talitha Cumi, Mulder starts to have more doubts over who his father is. Fox roams in his mother's house, full of accusations. "You had some kind of relationship with [...] the man who worked with my father, the man who came to you that night when I was 12 and forced you to choose Samantha. [...] You betrayed my father, your husband. [...] Who is my father?" Teena eludes a straight answer once more and feels insulted under the extreme weight of these accusations. The truth is that the CSM really was Mulder's father (7X04: Amor Fati). So what could have happened that night was that Bill had chosen Fox to be the one to be abducted (thus his name tag under Samantha's in the Strughold facility in 3X02: Paper Clip). But the Colonists had requested a genetic member of the Mulder family. At the hour of need, the CSM told the truth to Bill about Fox and his relationship with Teena, revealing to Bill that he was not Fox's real father. Bill was left with no other choice but to surrender Samantha. This revelation was strictly known to the CSM and Bill, nobody else knew of the CSM and Teena being the parents of Fox: it's a matter well hidden through all these years, even among fellow conspirators (see the Well-Manicured Man in Fight the Future) -- and it's a controversial matter that will still tease the audience for years to come. It is possible as well that Bill never learned the truth about Fox and about the CSM and Teena. Fox might have been chosen initially 'by default' as the first-born; then Bill made his mind up about his whole plan, as explained by the Well-Manicured Man in Fight the Future. That night he had to announce to Teena that one of her children would be taken away. Teena is devastated to learn that fact alone, no extra-marital revelations are necessary for all this fuss! In all cases it was not Teena's choice -- as she had half-confirmed to Fox in 3X02: Paper Clip: "You told me that when they took Samantha it was because you had to make a choice, but that's not how it happened. It wasn't your choice to make."
It's not surprising that Mulder goes to greater and greater lengths to learn the truth about his past and Samantha. His behaviour is increasingly compulsive and reaches a dangerous high point here -- as Scully says, "driving him more dangerously forward in impossible pursuit". If Mulder's obsession is with aliens, here they do not appear (apart from mixed images of the abduction from 2X01: Little Green Men). What the flashbacks are concerned with is human relations and non-supernatural phenomena. "It's all falling into place." This more rational approach is like a preparation for the ontological shock Mulder will receive in the next episodes: 4X24: Gethsemane and 5X02: Redux.
Mulder: "Scully, I don't want these symptoms to go away. Whatever's happening to me, whatever treatment I've received, is allowing me to go back into my unconscious. The truth is in there, recorded, and I've gotten access to it. What happened to my sister, the reason she was taken, it's beginning to become clear to me, and I need to know that."
Dr. Goldstein: "He said he was going to exorcise his demons."
Scully's report: "Agent Mulder undertook this treatment hoping to lay claim to his past. That by retrieving memories lost to him, he might finally understand the path he's on. But if that knowledge remains elusive, and if it's only by knowing where he's been that he can hope to understand where he's going, then I fear agent Mulder may lose his course, and the truths he's seeking from his childhood will continue to evade him, driving him more dangerously forward in impossible pursuit."