In 1859, Reverend McKim and his wife Sarah escorted Mary Brown, the wife of abolitionist John Brown, to Virginia, after his failed raid on Harpers Ferry. The McKims were accompanied in this effort by Hector Tyndale, another Philadelphia abolitionist. After visiting her husband in jail in Charlestown, Virginia [today Charles Town, West Virginia], Mary Brown, along with the McKims and Tyndale, stayed in Harpers Ferry until after the John Brown's execution on December 2, 1859. The McKims prayed and held hands with Mary Brown until the hour of execution passed. Afterward, they assisted her in claiming Brown's body and escorted her to Philadelphia; McKim continued with her to his burial place, the John Brown Farm in remote North Elba, New York, near present-day Lake Placid.