The following version of this book was used to create the guide: Miller, Sue. Monogamy. HarperCollins, 2020.

In Sue Miller's novel Monogamy, 29-year-old Annie, divorces her husband after realizing she does not love him. Seven years later, Annie meets Graham at the opening of his new bookstore in Cambridge, Massachusetts. They quickly fall in love, and marry only a year later. Prior to meeting Annie, Graham was married to Frieda. When their son, Lucas, was young, Frieda divorced Graham, tired of his promiscuity.

Almost 30 years later, Annie and Graham are still together. Graham has also continued his friendship with Frieda, and remained close to Lucas. Over the years, Annie also developed a kinship with Frieda, which she continues to cherish. However, Annie realizes her husband has grown increasingly distant. She hopes their upcoming dinner party will amend his strangeness.

Graham's odd behavior is due to his longtime affair with Rosemary. After consulting his old friend, Joh, Graham ends the affair. That night he feels better, and he and Annie make amends.

The next morning, Annie is shocked to discover Graham's dead body in bed beside her. She struggles to figure out how to respond, feeling inauthentic. After the EMTs remove him, she calls Frieda, Lucas, and her daughter, Sarah. In the days following, her family and friends try comforting her, but Annie feels no better. Sarah and Lucas are both frustrated that their mothers' sorrow is dominating their own. Finally, they convince Annie to have a memorial in the fall.

Six weeks later, Annie, Lucas, and Sarah scatter Graham's ashes at the family cottage in Vermont. Afterwards, they have a party at the bookstore, and a more intimate gathering at Annie's house. To Annie's surprise, the events cheer her. Her mood is spoiled, however, when she discovers Rosemary weeping in Graham's study. Seeing Rosemary's face, Annie realizes the truth of her relationship with Graham.

Annie confronts Frieda about the affair. Frieda admits she knew about it all along, but assures Annie it meant nothing. Annie is furious, her sorrow dominated by rage. She flees Cambridge for Vermont. However, the cottage brings no reprieve. Irritated by her mother's behaviors, Sarah returns to her home in California, in need of a new space to properly grieve her father.

Meanwhile, Frieda struggles to deal with her own emotions. She feels trapped by Annie's anger. Eventually she breaks the silence between them, realizing how much they need one another's friendship.

Shortly thereafter, Lucas and his wife, Jeanne, have a baby girl, Claire. Lucas becomes terrified that he cannot love his own daughter. While Jeanne and Claire are visiting Jeanne's family, Lucas has a dream about Graham. He takes it as a sign, and realizes his capacity to love.

Two years later, the family has healed. They share a holiday dinner together and reminisce. During the gathering, Lucas mentions the name of an author with whom Annie had a fling. When Lucas invites her to his reading, Annie wonders if something might happen between them. She soon realizes, however, that the man is confusing her with another woman. Feeling foolish, she flees. On her way home she is lost in thought and slips on the ice. When she wakes up in the hospital, she is momentarily convinced Graham is alive and will drive her home. That night she is grateful for her confusion, as it made her realize her continued love for her late husband.