"A New England Nun" is the story of Louisa Ellis, a woman who has lived alone for many years. Louisa is set in her ways, she likes to keep her house meticulously clean, wear multiple aprons, and eat from her nicest china every day. She has an old dog named Caesar who she feels must be kept chained up because he bit a neighbor 14 years ago as a puppy. Louisa promised Joe Dagget 14 years ago that she would marry him when he returned from his fortune-hunting adventures in Australia, and now that he has returned it is time for her to fulfill her promise. When Joe arrives, however, it becomes obvious that Louisa sees him as a disruption of the life that she has made for herself. When Joe arrives on one of his twice weekly visits, Louisa attempts to have a conversation with him, but is distracted when he tracks dirt on the floor, re-arranges her books, and accidentally knocks things over. The two have a cool and slightly awkward conversation when Louisa inquires after Joe's mother's health and Joe blushes and tells Louisa that Lily Dyer has been taking care of her. Clearly, she is only planning on marrying Joe because she promised that she would, since it would mean that Louisa would have to give up the life that she has made for herself.
Three weeks later, a week before the wedding, as Louisa is enjoying a moonlit stroll, she happens to overhear a conversation between Joe and Lily. Through this conversation, Louisa learns that Joe and Lily have developed feelings for each other in the short time that Joe has been back, and that Joe is in love with Lily but refuses to break his promise to Louisa. Lily supports Joe's decision, and though Joe encourages her to find someone else, Lily says, "I'll never marry any other man as long as I live."
The next day, when Joe comes to visit, Louisa releases Joe from his promise without letting him know that she is aware of his relationship with Lily. Joe and Louisa then part tenderly, and Louisa is left alone to maintain her present lifestyle.
The last line of the story is: "Louisa sat, prayerfully numbering her days, like an uncloistered nun."