In Horwitz’s telling, Brown was set on the road to Harpers Ferry from birth. His parents were fervent Calvinists who raised their children to see life as a constant struggle against sin. Much of the battle was personal: Brown’s earliest memory, from age 5, was of being whipped by his mother for having stolen a handful of brass pins. But it was political as well. The Browns believed that the devout had to bear witness against the sins of the nation. And there was no greater sin, they said, than the institution of slavery. So Brown’s father turned the family home in northeast Ohio into a stop on the Underground Railroad. And he turned his son into an ardent abolitionist.

Image John Brown in Boston in 1859, before the raid on Harpers Ferry. Credit... Library of Congress, courtesy of Harpers Ferry National Historical Park

Horwitz moves nimbly through Brown’s deepening involvement in the movement in the 1830s and ’40s, setting his devotion alongside the growing national conflict over slavery’s place in a country ostensibly dedicated to equality. Abolitionism was then dominated by pacifists like Garrison, who insisted that the evil could be destroyed by moral suasion. Brown didn’t agree. In 1837 he gathered together his wife and three teenage boys — the eldest of 20 children he would father — and asked who among them “were willing to make common cause with him in doing all in our power to ‘break the jaws of the wicked and pluck the spoil out of his teeth.’ ” From then on, one of his sons said, “there was a Brown family conspiracy to break the power of slavery.”

They got their first chance in 1856, when Brown and his boys joined the antislavery forces trying to prevent Kansas from entering the Union as a slave state. Brown’s vigorous defense of the free-state town of Osawatomie made him famous in the North, infamous in the South. But Horwitz lingers on a different action. On the night of May 24, 1856, Brown and four of his sons raided a tiny proslavery settlement on the banks of Pottawatomie Creek, not far from the Missouri border. There they killed and butchered five men, all of them violently opposed to abolitionism though not themselves slaveholders, slicing off their arms and splitting open their skulls with the broadswords Brown had brought with him for the occasion. “God is my judge,” he told another son upon their return. “We were justified under the circumstances.”

Not long after that, Brown began to plot the Harpers Ferry raid. His plan was to strike with 25 to 50 specially trained men, supply horses to between 80 and 100 slaves, swoop down on the armory and seize as many guns as possible and then escape into the surrounding Blue Ridge Mountains, from which they’d stage hit-and-run attacks meant to trigger a huge slave rebellion. It was a ludicrous idea, made all the worse by Brown’s mangled preparations. When he put it into operation in the autumn of 1859 with only 18 men in tow, the results were catastrophic. Horwitz describes the disaster in riveting detail. Brown and his men took the armory easily enough but got no farther. For 32 hours they were trapped inside while enraged townsmen laid siege to the place, picking off the insurgents one by one. A contingent of Marines finally put an end to it by battering down the armory’s doors, bayoneting two of the raiders and beating Brown senseless before taking him into custody.

At first even Brown’s fellow abolitionists thought it a mad affair. But when Virginia rushed him to trial — charged not only with conspiracy and murder but treason as well — Northern opinion switched, and then intensified when Brown bravely embraced the death sentence handed him. He went to the gallows hailed as a martyr, his execution marked by an extraordinary outpouring of grief. “Living, he made life beautiful,” Louisa May Alcott wrote on the day he died, “Dying, made death divine.” Horwitz wonders whether that may have been his intention all along, not to trigger a slave insurrection but to be defeated — and thus sacrifice himself to the cause. If so, he sacrificed 23 other people too, 16 of them killed in the raid, one dead of disease while awaiting trial, another six hanged for their involvement. Among the dead were two of his sons.