Manassas is the first book in a series of historical novels spanning the Civil War. The Brannon family of Culpeper County, Virginia - Abigail, a widow, and her four sons (Will, Mac, Titus, and Henry) and daughter (Cordelia) - work a good-sized, self-sufficient farm. The Brannons do not own slaves, but they are staunch supporters of the South in the conflict that is about to turn into war. Manassas centres around the lives of the Brannons in the winter and spring of 1861. As speculation grows that the North and South will soon be at war with each other, the Brannons have their own problems, not the least of which is the Fogarty clan, a large family of troublemakers in the area. Will Brannon is the county sheriff and kills one of the Fogartys while trying to arrest him for murder. Justifiable homicide or not, the Fogartys vow to avenge the loss of one of their own. While tensions mount in Culpeper County, news of Fort Sumter arrives. Will and two of his brothers join one of the Virginia militia units that quickly form. After a short period of training, the Brannons' unit is rushed to defend the village of Manassas, a strategic railroad junction.
When Union and Confederate armies engage in battle among the hillsides surrounding small, meandering Bull Run Creek, Will is forced to defend himself not only from the Union troops but also from the Fogarty brothers, who decide that the chaos of battle provides ideal circumstances for settling their score with him.