Shortly after returning to the farm, Tubman set out on her own, guided through the night by the North Star and well-worn paths of the Underground Railroad up into Pennsylvania, where slavery was illegal.

Tubman’s freedom proved to be bittersweet, as she would recount in her biography. In Philadelphia, she was free, working odd jobs, but lonely. Tubman began plotting her return home to bring her kin back with her: “I was free and dey should be free also. I would make a home for dem in de North, and de Lord helping me, I would bring dem all dere.”

In 1850, Tubman made her first trip back to Maryland, where, on the steps of the Dorchester County Courthouse (which was rebuilt in 1854 after a fire), Tubman’s niece, Kessiah, was scheduled to be auctioned off. But Tubman had plotted with Kessiah’s husband, who had been manumitted, to free his family. He secured the highest bid for Kessiah and their two children, smuggled them to a local safe house, then sailed up the Chesapeake to Baltimore, where Tubman greeted them and guided them to Philadelphia.

The rescue must have inspired Tubman. Over the next decade, she would return to Maryland’s Eastern Shore a dozen times, rescuing some 70 family members and friends.

Tubman was no-nonsense on these journeys, unwilling to suffer weakness among those joining her perilous flight. “For the faint of heart she carried a pistol, telling her charges to go on or die, for a dead fugitive slave could tell no tales,” Ms. Larson writes in her Tubman biography. “She used disguises; she walked, rode horses and wagons; sailed on boats; and rode on real trains...She bribed people. She followed rivers that snaked northward. She used the stars and other natural phenomenon to lead her north.”