Considered by Henry Green to be one of his best novels, Concluding tells the story of the strange events events that occur in a single day at a State-run school for girls. Retired scientist Mr. Rock, "an old man in love with his goose," lives in a cottage with his adult granddaughter Elizabeth. Bordering the grounds of the school, the cottage—which the State has given Rock for the duration of his life in gratitude for his scientific contributions—is coveted by the school's two spinsterish governesses, Misses Edge and Baker.

As the story opens, two students are missing. The resultant search for their whereabouts raises numerous fears and questions: have they been harmed? have they left on their own, alone? or have they perhaps been persuaded by the school's only male instructor, Sebastian Birt? how will the governesses keep the news from parents and State authorities until the girls have been found and an acceptable story contrived? will Rock report them for negligence? Meanwhile, as rumors and versions of the girls' disappearance spread through the school, and the governesses attempt to conceal their alarm by preparing for the school's tenth annual Founders Day Ball, the seemingly innocent proceedings take on an air of mystery, intrigue, and impending doom.