As Passing begins, Irene Redfield--a sophisticated and comfortably married woman of African-American descent--is opening her mail. She discovers a letter from Clare Kendry, an old acquaintance, and this document sets off a chain of memories. Irene recalls Clare's difficult childhood and cunning temperament, but is most preoccupied with a recent meeting between Clare and herself that had taken place two years before, in Chicago. The two women ran into one another purely by chance. However, the light-complexioned Clare explained a few of the more sensitive details of her life--in particular, the fact that she was "passing" as white.
Before the end of her stay in Chicago, Irene paid a visit to Clare's quarters. Here, Irene met Gertrude Martin, another African-American woman who could be mistaken for a white woman; Irene also encountered John Bellew, Clare's bigoted husband. Although the three women maintained their composure when Bellew voiced some of his demeaning opinions, Gertrude later expressed strong emotion over the boldness of Clare's version of "passing." For her part, Irene resolved never to communicate with Clare again.
However, Clare managed to reestablish contact with Irene. She sought out the Redfields in person, and bonded with the various members of the family. Clare's relationship with Irene's two sons was affectionate, and Clare also began to accompany Irene and Irene's husband, Brian, to upscale Harlem events. Irene was not fully comfortable with accepting Clare back into her life; in fact, Irene discussed the issue of racial identity with Hugh Wentworth, a white traveler and author who sometimes appeared in Harlem society. Yet Irene's discomfort intensified--and took on a new form--when it occured to her that Brian and Clare could be carrying on an affair.
Irene was determined to keep her marriage together, but soon a new disruption emerged. While shopping with a Harlem acquaintance, Felise Freeland, Irene encountered John Bellew. This chance meeting alerted Bellew that Irene was black. Although Clare's marriage might have been in serious danger, Irene remained quiet about her meeting and continued to accompany Brian and Clare to social functions, including a Christmastime party hosted by Dave and Felise Freeland. Yet Bellew tracked his wife to that location and created an uproar. Irene's recollections of the encounter between Clare and Bellew at the Freelands' party are spotty: Clare fell to her death from an open window, but it is not clear how exactly this catastrophe occurred. Bellew could not be found after Clare's fall, and the Freelands and Redfields spend the very end of the novel consulting with a mysterious man who is trying to figure out what had happened.