When four young men, slaves on Edward Gorsuch's Maryland farm, escaped to rural Pennsylvania in 1849, the owner swore he'd bring them back. Two years later, Gorsuch lay dead outside the farmhouse in Christiana where he'd tracked them down, as his federal posse retreated pell-mell before the armed might of local blacks--and the impact of the most notorious act of resistance against the federal Fugitive Slave Law was about to be felt across a divided...