The Three Stigmata of Palmer Eldritch by Philip K. Dick
The story begins in a future world where, as the dominant form of recreation, people take drugs to enter shared dream worlds. The worlds are based on "layouts," physical props in the real world that provide settings for the hallucinations. One of the top layout manufacturers is the New York City-based Perky Pat (or P.P.) Layouts, Inc.
The novel opens shortly after Barney Mayerson, P.P. Layouts' top precognitive, has been drafted by the UN to become a colonist on Mars. Mayerson is sleeping with his assistant, Roni Fugate, but remains bitter about his divorce from his first wife Emily, a ceramic pot artist. Meanwhile, Emily's second husband tries to sell her pot designs to P.P. Layouts as possible accessories for the Perky Pat virtual worlds -- but Barney, recognizing them as Emily's, rejects them out of spite.
Meanwhile, the UN rescues Palmer Eldritch's ship from a crash on Pluto. Leo Bulero, head of P.P. Layouts and an "evolved" human, hears rumors that Eldritch discovered an alien hallucinogen in the Prox system and plans to market it as "Chew-Z," with U.N. approval, on off-world colonies. This would effectively destroy P.P. Layouts. Bulero tries to contact Eldritch but he is quarantined at a U.N. hospital. Both Mayerson and Fugate have precognitions of Bulero murdering Eldritch.
Meanwhile, Emily and her second husband sell her pots to Eldritch and undergo evolution therapy. This causes Emily to devolve and unknowingly recreate pots she previously concocted.
Under the guise of a reporter, Bulero travels to Eldritch's estate on the Moon, where Eldritch holds a press conference. Bulero is kidnapped and forced to take Chew-Z intravenously. He enters a psychic netherworld over which both he and Eldritch seemingly have some control. After wrangling about business with Eldritch, Bulero comes to a seeming future Earth. Evolved humans identify him as a ghost and show him a monument to himself where he is to have killed Eldritch, an "enemy of the Sol System."
Bulero returns to Earth and fires Mayerson because Mayerson was afraid to travel to the Moon to rescue him. Mayerson, in despair, accepts his UN conscription to Mars but Bulero recruits him as a double agent. Mayerson is to inject himself with a virus after taking Chew-Z, which will deceive the UN into thinking Chew-Z is harmful and cause them to ban it.
On Mars, Mayerson buys some Chew-Z from Eldritch, who appears in holographic form. Mayerson tries to hallucinate a world where he is still with Emily but finds that he does not control his "hallucination." Like Bulero, he finds himself in the future. Mayerson arrives in New York two years hence where he speaks with Bulero, Fugate and his own future self about the death of Palmer Eldritch. He also encounters several manifestations of Eldritch, identifiable by their robotic right hand, artificial eyes, and steel teeth.
Eldritch offers to help Mayerson “become” whatever he wants. When a despairing Mayerson chooses death, he becomes one with Eldritch and Eldritch plans to allow him to die when Bulero kills Eldritch. Eldritch, meanwhile, intends to live on in Mayerson's form and enjoy the simple if arduous life of a Martian colonist. Mayerson, stuck in Eldritch's body and mistaken for him, is indeed nearly killed by Bulero in the near future, but before the fatal shot can be fired he is awakened from his Chew-Z trance in the present by Bulero, who has just arrived on Mars.
Bulero is willing to take Mayerson back to Earth but refuses to after learning that Mayerson did not inject himself with the virus. Mayerson is now confident that Bulero will kill Eldritch, so the sacrifice of taking the virus in order to ruin Eldritch's business is unnecessary; but he does not try to convince Bulero of this. Later, Mayerson discusses his experience with a neo-christian colonist and they conclude that either Eldritch became a god in the Prox system or some god-like being has taken his place. Mayerson is convinced some aspect of Eldritch is still inside him, and that as long as he refuses to take Chew-Z again, it is Eldritch who will actually be killed by Bulero in the near future; Mayerson is half-resigned, half-hopeful about taking on the life of a Martian colonist without reprieve. Mayerson considers the possibility of Eldritch being what humans have always thought of as a god, but inimical, or perhaps merely an inferior aspect of a bigger and better sort of god.
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