The story begins with the point of divergence in December 1860 by General David E. Twiggs bring unable to take command of the Department of Texas, which leaves Lieutenant-Colonel Robert E. Lee as the commander. The story itself is set in February 1861, shortly after the state of Texas voted to secede from the United States to join the Confederacy, to March 1861. Lee concludes that it is his duty to defend U.S. Army munitions and property in San Antonio, Texas, including the fabled Alamo, rather than to allow their surrender to the seceding Texas government, as Twiggs did in real life. That leads to a Second Battle of the Alamo.