Following John Brown's Harpers Ferry raid, Hoyt was recruited by Boston abolitionists to volunteer as a counsel to Brown, then on trial in Charles Town, Virginia (since 1863, West Virginia). He arrived at the trial on October 28, 1859, with orders to spy on the proceedings, pass messages to and from Brown, and, most controversially, to arrange a prison break that would free the prisoner and as many of his associates as possible. Because of the large number of soldiers and militia in Charles Town, and because Brown did not want to be rescued and refused to cooperate, Hoyt called off the plot.