On a rainy October night in 1859, violent abolitionist John Brown and a rag-tag band of young men descends on the federal arsenal at Harpers Ferry, Virginia. The raiders - made up of both whites and blacks and including two of Brown's own sons - plan to raid the arsenal, arm the local slaves, and spark a massive revolt in the South. But what begins as a lightning-strike gambit to grab guns and get out deteriorates into a three-day shootout that leaves two dozen dead and a young nation simmering over the "slavery question."
Brown, fresh from his bloody anti-slavery battles in Kansas and Missouri, had assembled 21 men in a farmhouse just five miles from town to plot the raid two months earlier. But now inside the Ferry, the plan quickly unravels. The local militia is summoned and the area's slaves fail to join Brown's fledging army. Against the wishes of his men, Brown decides to wait for the slaves to appear - a fatal error that transforms a stealth operation into a desperate bloodbath.
As avenues of escape dwindle, and the raiders are cut down one-by-one, they hear the sound of marching. Elated, Brown believes that his slave army has finally arrived. Instead, he finds himself face-to-face with Colonel Robert E. Lee and a regiment of US Marines, poised for the final assault.