The Sunday War chronicles the lives of a German soldier and a Russian family starting in 1933 with the rise of Hitler in Germany and the start of the Great Terror in the Soviet Union, as author Robert Conquest termed it.

Industrial crane operator Herman Heitz is impressed into a military security unit near Munich after he tries to learn the fate of a Jewish supervisor, who was whisked away by the new Nazi regime in 1933. Rising to the rank of sergeant, his unit unwittingly provides security for an SS unit in 1941 as SS soldiers conduct pogroms against Russian Jews in eastern Poland and later White Russia, then provides anti partisan hunting support before transforming into a desperately needed antitank gun battery.

Sergei Zalovskiy is a member of the elite NKVD, who finds himself imprisoned in Siberia in 1937, then released in time to face the German onslaught in June 1941. He is assigned as a rifle division commander to battle the German Army in southern Russia as well as the NKVD, before gaining an assignment which takes him into his hometown, where is wife and daughter may be trapped.

Both families fight not only the ruthless enemies they face, but also the ruthless leaders who lead them to war.