Oedipa Maas is a typical suburban housewife in 1960s California. She is introduced to the audience as she returns from a Tupperware party and then prepares her husband's dinner. Once she is made executor of Pierce Inverarity's estate, however, she is thrown into a world of strange conspiracies. As she begins to piece together the estate and the nature of society itself, Oedipa engages in an act of pattern recognition and interpretation. She begins to see familiar faces, shapes, and ideas as they recur in vastly different contexts. The Tristero mail system, the muted post horn, and other ideas and institutions repeat throughout the novel. They become like symbols in any novel, except these ones are difficult to interpret and seem only to multiply as Oedipa recognizes them.

Once Oedipa sees them, she begins to notice them everywhere. Conspiracies are rampant throughout the text. From wars fought between competing mail services to right-wing organizations such as the Peter Pinguid Society, Oedipa comes to realize that her simple domestic life bore little resemblance to the realities as experienced by other people. The contrast between the unassuming domesticity of Oedipa at the beginning of the novel and the fraught, distressed investigator who attends the auction demonstrates the dangers of pattern recognition.