Based on an actual person, Broken Drum is the story of Charley King, a twelve-year-old drummer boy from West Chester, Pennsylvania, who is caught up in the excitement and patriotism during the early stages of the Civil War. Mustered into Company F of the Pennsylvania 49th Volunteers in September 1861, his journey begins with the defense of Washington as part of Major General George McClellan's Army of the Potomac. Charley is involved in the transport of that huge army down the Potomac River and Chesapeake Bay to Norfolk, and then, by land, the grueling progression of the Peninsula Campaign and its disappointing retreat, eventually arriving at the Battle of Antietam.

His journey also takes him from childhood to maturity. Not only is he exposed to the excitement and horrors of battle, but also to the boredom of picket duty, endless drills, epidemics, and inclement weather. During his intense experiences, Charley meets many diverse characters, both real and fictional. Among the historic characters are President and Mrs. Abraham Lincoln, General McClellan, and Clara Barton.