Sula's return to the Bottom is accompanied by a "plague of robins." Her stylish, expensive clothing startles her old neighbors. When she visits Eva, their encounter quickly becomes antagonistic, as Eva criticizes her for remaining unmarried. Angered by Eva's judgmental statements, Sula orders her to shut up. She says that Eva's decision to cut off her own leg in order to collect insurance does not give her the right to control other people's lives. When, in response, Eva insinuates that Sula was a bad daughter, Sula accuses her of murdering Plum. Eva reminds Sula that she watched Hannah burn to death. Sula threatens to kill Eva in the same way Eva killed Plum. Frightened, Eva keeps her door locked at night. Not long afterward, Sula becomes Eva's guardian and commits her to a nursing home, shocking the entire community. They decide that Sula is truly evil, though Sula tells Nel that she put Eva in a home because she was afraid of her.
Sula and Nel begin to once more spend time together. One day, when Jude returns home and complains to Nel about some minor annoyance at his job, Sula teases him. Irritated, he comments that her birthmark looks like a snake. This early animosity, though, eventually leads to an affair. After Nel discovers the affair by stumbling on Sula and Jude having sex, Jude abandons Nel and their children. Nel is devastated by the betrayal of her husband and best friend.
Sula breaks with social convention twice in this section: first, when she puts Eva in a nursing home, and again when she has an affair with Nel's husband. Her unpredictable behavior frightens the already suspicious community of the Bottom. In order to contain and understand their fear, they label her "evil." Like Eva, they impose order on her influence by retroactively imposing connections on seemingly unrelated events. The "plague of robins" becomes an evil omen of her return.
Considering Eva's own unconventional life, it is odd that she criticizes Sula for not following the conventional path. She criticizes Sula for remaining unmarried when she and Hannah never remarried. She and Hannah were fiercely independent, yet she criticizes Sula for her independence. Perhaps Eva's strange reversal of attitudes derives from her need to contain what she perceived as Sula's influence in Hannah's death. Eva and Hannah were not considered serious threats to the social fabric whereas the entire community, including Eva, considers Sula a threat.
It is also entirely possible that Eva does not want Sula to threaten her matriarchal control over her household. In some ways, Eva does believe that her sacrifice for her children gave her the right to control their lives. She did kill her own son partly because he did not fulfill her expectations. The Deweys gained a fierce attachment to one another by virtue of Eva's decision to name them all Dewey. However, they never grew to adult size, and they never developed independent identities. Perhaps Eva is unable to ever regard her children as full adults who can make their own decisions.
Sula's total disregard for the social rules governing marriage nearly destroys Nel. As a result of his extramarital tryst, Jude abandons his family for good. Although Sula's actions were selfish, it is important not to be seduced by the community's need to define her as an evil person, as their decision to place all the blame for the failure of Nel's marriage on Sula is rather facile. After all, Jude also chose to take part in the affair, and it was he who chose to leave his family. Sula did not force him to abandon his family. But because Sula remains in the Bottom, the community finds it much easier to concentrate their antagonism on her.
Nel's devastation is partly due to her weak sense of self. She always viewed her marriage as a combination of two halves of the same self. Nel cannot even cry after the end of her marriage. She did everything that social convention demanded, but she was still abandoned by her husband.