In the mid-1960s, Oedipa Maas lives a fairly comfortable life in the (fictional) northern Californian village of Kinneret, despite her lackluster marriage with Mucho Maas, a rudderless radio jockey and ephebophile and her sessions with Dr. Hilarius, an unhinged German psychotherapist who tries to medicate his patients with LSD. One day, Oedipa learns of the death of an ex-lover, Pierce Inverarity, an incredibly wealthy real-estate mogul, who has left her as the executor of his estate. Inverarity appears to have owned or financed nearly all the goings-on in San Narciso, a (fictional) southern Californian city near Los Angeles. Oedipa goes to San Narciso to meet Inverarity's lawyer, a former child actor named Metzger and they begin an affair, which fascinates a local teenage rock band, The Paranoids, who begin following them voyeuristically. At a bar, Oedipa notices the graffiti symbol of a muted post horn with the label "W.A.S.T.E." and she chats with Mike Fallopian, a right-wing historian and critic of the postal system, who claims to use a secret postal service.
The novel's ubiquitous muted post horn symbolIt emerges that Inverarity had Mafia connections, illicitly attempting to sell the bones of forgotten U.S. World War II soldiers for use as charcoal to a cigarette company. One of The Paranoids' friends mentions that this strongly reminds her of a Jacobean revenge play she recently saw called The Courier's Tragedy. Intrigued by the coincidence, Oedipa and Metzger attend a performance of the play, which briefly mentions the name "Tristero". After the show, Oedipa approaches the play's director and star, Randolph Driblette, who deflects her questions about the mention of the unusual name. After seeing a man scribbling the post horn symbol, Oedipa seeks out Mike Fallopian, who tells her he suspects a conspiracy. This is supported when watermarks of the muted horn symbol are discovered hidden on Inverarity's private stamp collection. The symbol appears to be a muted variant of the coat of arms of Thurn and Taxis, an 18th-century European postal monopoly that suppressed all opposition, including Trystero (or Tristero), a competing postal service that was defeated but possibly driven underground. Based on the symbolism of the mute, Oedipa thinks that Trystero exists as a countercultural secret society with unknown goals.
She researches an older censored edition of The Courier's Tragedy, which confirms that Driblette indeed made a conscious choice to include the "Tristero" line. She seeks answers through a machine claimed to have psychic abilities but the experience is awkward and unsuccessful. As she feverishly wanders the Bay Area, the muted post horn symbol appears among an engineer's doodles, as part of children's sidewalk drawings, amidst Chinese ideograms in a shop window and in many other places. Finally, a nameless man at a gay bar tells her that the muted horn symbol simply represents an anonymous support group for people with broken hearts, Inamorati Anonymous. She witnesses people referring to and using mailboxes disguised as regular waste bins marked with "W.A.S.T.E." (later suggested to be an acronym for "We Await Silent Tristero's Empire"). Even so, Oedipa sinks into paranoia, wondering if Trystero exists or if she is merely overthinking a series of false clues with no definite connections.
Fearing for her sanity, Oedipa makes an impromptu visit to Dr. Hilarius, only to find him having lost his own mind, firing a Gewehr 43 randomly and raving madly about his days as a Nazi medical intern at Buchenwald. Hilarius now thinks that Israel-sponsored Nazi hunters are after him for his crimes, and he cannot overcome his mental horror about the fact that he once supported Freud, a Jew. She helps the police subdue him, only to return home to find that her husband Mucho has lost his mind in his own way, having become addicted to LSD. Oedipa consults an English professor about The Courier's Tragedy, learns that Randolph Driblette has mysteriously committed suicide, and is left pondering whether Trystero is simply a prolonged hallucination, a historical plot, or an elaborate practical joke that Inverarity arranged for her before his death. Oedipa goes to an auction of Inverarity's possessions and waits on the bidding of lot 49, which contains the stamps which are thought to refer to Trystero. Having learned that a particular bidder is interested in the stamps, she hopes to discover if this person is a representative of the Trystero secret society.
