A Month in the Country is the story of a World War I survivor named Thomas Birkin. Birkin travels to the small town of Oxgodby in the summer of 1920. He has been hired as part of a townsperson's will to uncover and restore a medieval wall painting in the church's arch. He arrives in Oxgodby, scarred by his experiences in the war and unwanted by the church's priest. He also knows not a soul in town.

As Birkin sets up living quarters in the church's bell tower, he begins working on uncovering the painting. He meets several townspeople. Moon, a war survivor, has been hired by Miss Hebron's executors to find a lost grave in the meadow next to the church. He and Birkin find an immediate friendship. They share their morning tea together and discuss their tasks and experiences. Birkin also befriends two females: Kathy Ellerbeck, a fourteen-year-old girl and Alice Keach, the priest's wife. He begins to fall in love with Alice. They share an unspoken and unconsummated love. Birkin senses several moments in which he could have acted, thus changing the course of their lives.

As Birkin works on restoring the painting, he experiences a deep sense of communication and contentment within his rural surroundings. His face twitch, which developed during the war, almost fades away. Mentally, Birkin feels happy and fulfilled. He is content and proud of his work. The painting itself leaves several questions in Birkin's mind: why a second painter appears to have finished the part of the painting depicting hell's fires and whether one of the damned was a real person from the parish. As he works, Birkin ponders these questions and marvels at the skills of the original painter.

As times goes on, Birkin finds himself drawn more and more into the community. His feelings of contentment deepen. He watches Moon plot out the outlines of an ancient basilica. He talks about a variety of topics with both Kathy and Alice. He also finds himself in unexpected places, including a church picnic and preaching in a neighboring town church.

As the novel ends, Birkin realizes that the original painter fell to his death in the church before finishing the painting. When Moon uncovers the lost grave, they also realize that the damned man in the painting is none other than the excommunicated ancestor of Miss Hebron. When Alice arrives to see, they share a moment where their love is almost spoken, but not acted upon. In the end, neither crosses the line. Alice leaves Oxgodby with her husband the next day. Birkin receives a letter from his estranged wife and decides to return to her. After gazing on the painting one last time, Birkin leaves Oxgodby and his time there comes to a close.