The Machine Gunners takes place in 1941 in Garmouth, a small coastal town in northern England. World War II has begun to intrude in the lives of the townspeople. The sound of guns sends them running, panic-stricken, to their bomb shelters; when the bombings cease, the people return to the streets to confront the horrors of destruction.

Fourteen-year-old Chas McGill's feelings of helplessness in the face of the German soldiers and his sense that God has abandoned him compel him to take control of his life. Thus, much of the story takes place in and around an elaborate underground shelter built by Chas and his schoolmates. The fortress, hidden beneath a bombed-out house and equipped with a captured German machine gun and provisions for Chas's circle of trusted friends, serves as the only place where the children feel powerful and safe.