The Dulcimer begins when twelve year old Jeremiah Brewster and his cousin, Tommy, hear that the Union army has taken the railway town of Chattanooga. Fearful that their tiny mountain hamlet of Hemlock Hollow will be next, they go in search of the Confederate army. They catch up with the Rebels on the floodplain of Chickamauga creek and blunder into one of the bloodiest battles of the Civil War. Jeremiah is saved from death by an Irish immigrant and Union soldier, Michael Flannery. Guilt ridden by the death of a boy of similar age and appearance in the old country, Michael carries the injured Jeremiah with him as the defeated Union army retreats to Chattanooga. There, for the first and only time, the Union army is besieged by the Rebel army on the surrounding mountains. Their supply lines are cut and they come close to starvation. Jeremiah must now share the fate of his captors and the civilians left trapped in the city as they struggle to survive and maintain their humanity and decency amid the horrors of war. The story weaves back and forth between the terrors of the battlefield and the complications of human relationships in the crucible of a city under siege.