The entire novel S. is told in the voice of Sarah Worth as represented by letters and tapes mailed to relatives and friends from a motel near the Arizona commune. Other voices enter only when Sarah reports conversations in her letters or happens to catch the guru's voice on her tape recorder. The main character is thus a narrator whose point of view dominates the novel, but her limited understanding is apparent, and the reader must look between the lines for the truth of what is happening.

Sarah Worth is modeled after Hester Prynne, the heroine of Nathaniel Hawthorne's The Scarlet Letter (1850). She has a daughter named Pearl, a husband who is a physician, and a mother descended from the Prynne family. As a modern character, however, she also has a dentist, a lawyer, and a hairdresser. What she needs, of course, is the fulfillment of heart and soul that also fascinated and eluded Hester Prynne. Adultery with a pious hypocrite, as Hester discovered, only compounds the feeling of loss and despair. Sarah also wanders "in the dark labyrinth of mind," and like Hawthorne's character finds "a home and comfort nowhere."

At the religious commune Sarah is given the name "Kundalini" which Updike defines as "coiled up" or "the serpent of female energy." Sarah has left her husband at the beginning of the novel in part to assert her independence and feminine power, but in Arizona she finds several women competing for the attention of their supposed religious master. She learns more about jealousy and seduction than any promised form of enlightenment, but she does have an affair with the guru before discovering that he really comes from Boston. After liberating herself from him at the end of the novel, Sarah is still unable to sort out the needs of flesh and spirit. At least she is not without material resources. Several pieces of inherited silverware are thought about with comic regularity, and she does manage to embezzle hundreds of thousands of dollars from the Treasury of Enlightenment.

The other important character in the novel is the cult leader, Updike's contemporary version of Arthur Dimmesdale. Sarah commits adultery with Art Steinmetz for two reasons: She thinks he radiates divine power, and on a deeper level she may feel that he is a replacement for the Jewish boy her parents would not allow her to marry in the first place. Art is a chameleon who presents himself as the Arhat, or "deserving one," who claims to have reached a high level of enlightenment. His particular deserts include women, limousines, and the power of religious language. Sarah and Hester, no doubt, are attracted to their men of God because sex and religion are twin expressions of their desire for satisfaction and fulfillment. Both find a mixture of faith and hypocrisy because the false saviors are designed by male authors to attract and disappoint their frustrated heroines.