After her strange encounters following a W.A.S.T.E. mailman and dancing with deaf-mutes in a hotel, Oedipa decides that it is time to return to Kinneret and her husband. She wants to see a psychiatrist and, in fact, resolves to meet with Dr. Hilarius in the hope that he will tell her that she simply dreamed everything; in other words, Oedipa wants to be told that the Tristero mystery is a figment of her mind. However, as she arrives at Hilarius' house, someone begins to fire shots at her. She runs toward the house after Nurse Helga Blumm lets her in. The Nurse tells Oedipa that Hilarius has gone insane. He has locked himself in his office with his rifle and is shooting at everyone and everything. Apparently, Hilarius believes that three men with sub-machine guns are out to get him. Oedipa goes to the office and speaks to Hilarius through the door. He tells her that he once trusted Freud, but he no longer believes his theories. Hilarius also makes it clear in his language that he dislikes Jews.
Meanwhile, the cops arrive at the house, and Oedipa tries to convince Hilarius not to shoot at them. Hilarius, however, suspects that the officers are agents of Freud who deserve to die. Hilarius also confirms that he is not on LSD. As the police enter the house, Hilarius opens the door and pulls Oedipa into the office. He tells her about a face he likes to make that has been known to devastate people's psyches. He then admits that he worked at the Buchenwald Nazi concentration camp for the Nazis, inventing drugs that would render Jews permanently catatonic. Hilarius now thinks that Israel is after him for his crimes, and he cannot overcome his mental horror about the fact that he once supported Freud, a Jew. Meanwhile, Oedipa takes his gun, which he had set down, and points it at him, making Hilarius think that Oedipa has come to kill him. She tells him otherwise, to which he responds that Oedipa ought to cherish all fantasies because fantasies are what distinguish us as humans.
Oedipa tells the cops to break down the door. They barge into the room and apprehend Hilarius. At this point, Oedipa notices that a number of news crews have gathered outside to cover the event, and, in fact, she notices that her husband Mucho's van from the KCUF station is parked outside. She goes down to see Mucho and delivers a live account of what happened over the airwaves. Later, she and Mucho go back to the studio and chat. Mucho boasts briefly about his tone-separating ability, but it quickly becomes clear that he is tripping on LSD, which he is beginning to take on a regular basis. LSD, he explains, takes away the nightmares he once had about the empty car lot. Oedipa later goes back to San Narciso, realizing that she no longer knows her own husband.
The final segment of chapter five presents a somewhat esoteric character study of Dr. Hilarius, a man who has clearly lost his mind. He is a good example of a character haunted with guilt about his past, leading him to believe that he is being persecuted. Hilarius is an extreme example of the isolated character that Oedipa slowly becomes. While Oedipa never falls so hopelessly into despair as Hilarius, she does show the same tendency to become divorced from her surroundings.
This final section also details how Oedipa becomes emotionally, spiritually, and intellectually separated from Mucho, her husband. Mucho has become a victim of the world of LSD, forcing him to withdraw from standard human interaction and substantially changing his life to the point where Oedipa does not even feel as though she knows him.
It is interesting and troubling to note that Oedipa loses these former soul mates through no real fault of her own. It is Hilarius' regression into insanity and Mucho's use of drugs that pull them both away from her and the rest of the world, but these are factors over which Oedipa has no control. She is, in essence, socially helpless, lying prey to the caprice of the minds and actions of others. One of the curious questions in the novel is how Oedipa manages to stay intellectually and psychologically stable in the midst of all the decay and chaos floating around her.