The novel opens with an "Editors' Note," claiming that the following pages were found among the papers of Antoine Roquentin. The pages are presented in a diary format. The Editors suggest that Roquentin began his diary in January 1932, following his return from the Far East, Central Europe, and North Africa. He moved to the seaside town of Bouville in order to write a book about the Marquis de Rollebon.
Roquentin's introductory notes establish his intent to keep a diary. He feels that something has changed in the way he sees objects, but he cannot quite place his finger on exactly what. He hopes that a diary will help him better understand what is going on, specifically, to see, classify, and determine the extent and nature of the change. He recalls an odd sensation while holding a stone a few days earlier, but is not sure whether the odd feeling came from the stone or himself. Despite his feelings of disgust and being afraid of the stone, he is wary of exaggerating the events he records in his diary. Indeed, he soon writes that his odd feelings were nothing but a passing moment of madness and that there is no longer any need to continue with his diary.
Nevertheless, the next entry, dated January 29, 1932, opens with Roquentin's realization that something strange has happened to him. He first thought that it was nothing but a "passing moment" gives way to a permanent feeling of uneasiness around objects and people. He hopes that it is nothing but an "abstract change," but soon begins to worry that he is the one who has changed little by little, overwhelmed by a sudden transformation. He recalls his whimsical decision to leave Vietnam and return to France, terrified that it was actually a precursor to his current state of mind.
The next day, however, he becomes resigned to his fate, realizing that his solitary lifestyle has changed him. He notices that living alone has prevented him from both having friends and simply communicating with other people. When he looks inside himself for answers, he finds nothing. Even when he has sex with Francoise, a local barmaid, very little is said between them: Roquentin feels that he is purging himself of a "certain nostalgia" rather than feeling pleasure. Yet he does acknowledge that he would be lying to himself if he began to think that nothing new has happened to him. When he looks at a glass of beer or a soggy piece of paper lying in the street he is unable to touch them despite his desire to do so. He does not feel free. Thinking back on the strange feeling he had while holding the stone he recalls a "nausea of the hands."
Roquentin attempts to divert his angst with historical research on the Marquis de Rollebon, a mysterious aristocrat who lived around the time of the French Revolution. Yet Roquentin's research begins to bore him. Ten years earlier he had been fascinated with the story of the Marquis, but now feels that he is writing a work of pure conjecture that has nothing to do with the real Marquis at all. His work inevitably returns Roquentin to himself and his emerging disgust at the outside world. Specifically, the changing appearance of objects in the light of the sun makes him feel uneasy. When he tries to focus on the mystery of Rollebon he can't help but look at himself in the mirror, alarmed that he doesn't recognize his own face.
Existentialism is primarily a reaction against the traditional philosophical approach to objective and abstract understandings of human behavior. Instead, existentialists choose to study individual human beings who exist independently of cultures, traditions, and laws. As Sartre stresses in the "Editors' Note," not only have Roquentin's writings not been altered, but they are his personal papers. This establishes the novel's focus on one singular individual through the lens of his most personal documents. As such, they are an accurate reflection of one person and nothing else--the main focus of existentialist thought.