Warning: Wikipedia contains spoilers
The story is a horrifying vision of a God that is all-devouring and amoral, and is a sharp depiction of religious despair that prefigured Dick's own later crisis of faith and mental breakdown.
The story's protagonist, Tung Chien, is a party bureaucrat in Vietnam in a future where Chinese-style communism has triumphed over the entire world. The atheist Communist Party rules absolutely over a population that is kept docile by hallucinogenic drugs.
Given an illegal drug by a street seller, he sees the Party leader's appearance on television as an horrific hallucination. He later learns that the drug is stelazine, an anti-hallucinogen, and that what he sees is the true reality of the Party leader: or at least one of them, because different people see any one of twelve different possible visions of the leader. Some see a machine ("the Clanker"), other see a biological monstrosity ("the Gulper"), yet others see a whirlwind, and so forth.
An underground movement, fearing that the leader is not human, contrives to place him at a party where the leader will be present. He meets the leader, who is apparently an undistinguished middle-aged man, and takes the anti-hallucinogenic drug.
He learns that all the visions are true, and far more besides, as the Party leader is not only not human, but God itself.
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