Laurent visits the Raquins’ apartment almost every evening, and not only because he must complete Camille’ portrait. He is delighted by the good, free food and the comfortable atmosphere. And Thérèse is clearly attracted to the new guest; as Laurent works, she watches attentively. Laurent considers whether or not to take Thérèse as a lover. Finally, he decides in favor of an affair; other women are too expensive, and Camille is no threat.
The portrait is at last finished, much to the pleasure of Camille and Mme Raquin. Camille even decides to buy celebratory champagne, leaving Laurent and Thérèse alone for a brief moment. This small opportunity is all Laurent needs; he grasps Thérèse, and despite the young woman’s initial resistance, the two make love swiftly and brutally before Camille’s return.
So begins the long, tense, exhilarating affair between Thérèse and Laurent. The two lovers arrange secret meetings in Thérèse’s bedroom during the day; Laurent finds excuses to leave work, and Thérèse leaves Mme Raquin to attend to the shop. Changes take place in the lovers, too. Intrigued but also unnerved by his wild new mistress, Laurent begins to see Thérèse as truly beautiful. And Thérèse reveals her deep-seated resentment for Camille and Mme Raquin, who subjected her to such a closed upbringing and offered her a life with so few possibilities.
Thérèse also adopts a more reckless attitude. Though Laurent is genuinely afraid that Mme Raquin will discover the affair, Thérèse brushes off this possibility and seems to enjoy deceiving the old woman. Laurent (who comes from superstitious peasant stock) is also unnerved by François, Mme Raquin’s watchful cat, while Thérèse treats François as simply a comical, ridiculous presence.
For once, all is well in the Passage du Pont-Neuf. Laurent enjoys the warm and reassuring atmosphere of the shop, and is on the best of terms with the entire Raquin household: doted on by Mme Raquin, admired by Camille, and cherished passionately by Thérèse. Thérèse herself feels calm, and revels in feelings of superiority to her aunt and husband, whom she has managed to deceive so deftly. She even uses the long-despised Thursday evenings to set new lovemaking sessions with Laurent. This state of supreme satisfaction lasts for eight months.
One day at his office, Laurent is informed that he will lose his job if he takes any more time off. He realizes, with anguish, that this will keep him from seeing Thérèse and will lead to the end of his affair. Thérèse is informed of the new conditions later in the day by Laurent himself. Desperate herself, Thérèse tries to secure new meetings with Laurent, but the young man proceeds to break each newly-appointed rendezvous.
Finally, Thérèse finds an excuse to leave Mme Raquin’s shop one evening, with the intention of visiting Laurent in his apartment. Thérèse finds Laurent in the tiny garret room where he lives. And this meeting proves fateful. After indulging their passions, Thérèse and Laurent consider their options. Laurent is overcome with devotion, and tells Thérèse that he dreams of spending an entire night with her and waking up beside her. But throughout his speeches, he drops hints that Camille could go on a “journey” or succumb to an “accident.” As soon as Thérèse leaves, Laurent realizes that he is determined not to give her up and that murdering Camille - an idea that had only just occurred to him - might be an effective way of securing the comfortable life he wants. Even Thérèse, when she gets home, feels murderous impulses toward the sleeping Camille.
Though Laurent continues to frequent the shop in the Passage du Pont-Neuf, he only exchanges the smallest, slyest affections with Thérèse whenever they are alone. Otherwise, Thérèse has returned to her moody ways. Yet the Thursday evening guests continue to find sources of amusement and diversion, including the stories of crime and criminals told by Old Michaud.
As Old Michaud explains to the guests one evening, there are numerous crimes that go undetected and numerous murderers who escape justice. This assertion shocks and frightens Grivet, who wants to believe that justice can be flawlessly administered. Thérèse and Laurent have their own reaction to Old Michaud’s tales of unresolved crimes; they look right at one another and seem to tingle with anticipation.
It is one of Camille’s habits to go out walking in Central Paris on Sundays, often with Thérèse for company. Yet on one particularly beautiful Sunday, Camille, Thérèse, and Laurent decide to make an excursion to the countryside just outside the city, where they can enjoy the scenery and eat a meal together. They arrive at the islands around Saint-Ouen at about midday, and Camille falls asleep in a shady, tree-lined clearing. Laurent once again feels affinity for Thérèse and once again contemplates murdering Camille; he raises his foot over the sleeping man’s head, yet decides against a move that would be so bloody and leave such irrefutable evidence.
Camille awakens, and is delighted to find Laurent in a good humor. Camille and his companions then make their way to an eating house, where they order dinner, and decide to rent a boat. Yet the boat that Laurent picks out is light, and could easily tip over. However, Laurent coaxes both the reluctant Camille and the increasingly distressed Thérèse into the small boat. Thérèse knows what Laurent is planning; despite moments of hesitation, she decides to go along with his scheme.
Once the boat drifts out of sight and behind some islands, Laurent sets the murder in motion. He grabs Camille by the neck, begins to strangle him, and manages to throw him into the river, but not before Camille wounds Laurent - biting into Laurent’s neck and tearing away a piece of his flesh. Thérèse faints as she watches her husband struggle. Once Camille is in the water, he tries to swim but, weakened, sinks after a few attempts. Laurent then grabs the unconscious Thérèse, knocks over the boat, and alerts a party of oarsmen to the presumed accident. He then returns to shore and, after leaving Thérèse at a nearby restaurant, sets off for Paris to tell Mme Raquin the horrible news.
In the course of these chapters, Laurent begins an affair with Camille’s wife and is driven to murder Camille himself. It would be wrong, however to identify Camille as Laurent’s antagonist. Laurent is “on intimate terms with Camille, but felt no anger or remorse towards him,” and murders Camille mostly to remove an obstacle, to ensure himself the life of sensual pleasures and financial stability that he believes Thérèse - and her inheritance - will offer (42).
Thérèse and Camille are a different story; here, there is a clear protagonist-antagonist relationship, though Camille himself is fatally unaware of Thérèse’s hostile feelings. For the first time in the novel, Thérèse voices her long-lived resentments in detail. She tells Laurent of her infuriating, stupefying upbringing: “Oh, what a childhood I had! I still feel revulsion and outrage when I remember the long days I spent I that room with Camille gasping away” (37). Because Laurent and Thérèse can only make love in Mme Raquin’s apartment, Thérèse is (ironically enough) still trapped in Camille’s room. She is enlivened by love, but still cannot escape her limitations and resentments.
However, these chapters do entail a rare departure from the Passage du Pont-Neuf. For the first time, we are given a direct look into the miserable lodging house Laurent rents, occupying a garret apartment that Zola compares to a "hovel" and a "hole." Thérèse enters this space and finds that it is "so small that her wide skirts could hardly fit inside it" (47). The problem that Laurent and Thérèse face may not simply be one of social boundaries and frustrated hopes; whether they know it or not, the closed and cramped settings that they both inhabit may be driving them to a state of restless, keyed-up fury.
Ultimately, Laurent is driven to murder Camille by his own frustrations, by his craving for Thérèse: “A raging of the blood had infected his flesh and now that his mistress was being taken away from him, his passion burst out with a blind fury” (46). On the basis of such irrational instincts, it would be natural to expect Laurent to commit a reckless and impassioned crime - yet he does just the opposite. He carefully thinks through all his options and takes precautions to avoid detection. He even briefly considers killing Camille using a blunt and bloody act of violence - raising his foot to crush the sleeping Camille’s head - but is rational enough to see how easily this murder would be solved.
The murder that Laurent commits is a flawless piece of savagery: it looks like an accident and leaves no incriminating clues. Laurent even leaves the impression that he had ardently and heroically tried to save the drowning Camille. Although Zola constantly points out how different Thérèse and Laurent are in temperament, the two protagonists have found one major point of similarity by the end of this chapter. They have both become proficient in the art of deception.