In early September 1862 thousands of Union soldiers huddled within the defenses of Washington, disorganized and discouraged from their recent defeat at Second Manassas. Confederate General Robert E. Lee then led his tough and confident Army of Northern Virginia into Maryland in a bold gamble to force a showdown that could win Southern independence. The future of the Union hung in the balance. The campaign that followed lasted only two weeks, but it changed the course of the Civil War. D. Scott Hartwig delivers a riveting first installment of a two-volume study of the campaign and climactic battle. It takes the reader from the controversial return of George B. McClellan as commander of the Army of the Potomac through the Confederate invasion, the siege and capture of Harpers Ferry, the daylong Battle of South Mountain, and, ultimately, to the eve of the great and terrible Battle of Antietam.