On December 20, 1860, a momentous occasion takes place in the beautiful, graceful old city of Charleston, South Carolina. A secession ordinance withdrawing South Carolina from the Union is signed in Institute Hall, and a festive celebration erupts throughout the city. At least in the minds of most of its citizens, South Carolina is now a sovereign nation.

Taking part in this celebration are cadets from the Citadel, a military institute for young men. Two of these cadets are Robert Gilmore and Allard Tyler, who are good friends despite differences in their backgrounds. Allard is from a wealthy Charleston ship-building family, while Robert is from a much less well-to-do farm family. Stirred by the patriotic fever that grips Charleston, both young men vow that if secession leads to war with the North, they will withdraw from the Citadel and join the battle against the Yankees.

Robert remains in Charleston over the Christmas holidays, partly because he does not have the money to make the trip home and partly because of his interest in Jacqueline Lockhart, daughter of a wealthy plantation family. Allard is interested in Diana Pinckston, the daughter of one of his instructors at the Citadel.

The stories of these young people and their friends and families play out against a backdrop of secession fever and the drumbeat of impending war. Robert and Allard are among the cadets manning the guns when the Star of the West attempts to bring supplies and reinforcements to Fort Sumter. Both immediately withdraw from the Citadel, Robert enlisting in the Hampton Legion and Allard intending to join the Confederate navy. Robert sees his first action at the battle of Manassas in Virginia, and Allard, who has joined a privateer attacking Northern Virginia merchant vessels, barely escapes with his life when his ship is sunk during a battle with a Union cruiser. For both young men, many of their romantic notions about the glory of war are shattered.