Soul Catcher by Michael White

Augustus Cain is a man with his back against the wall. A war-scarred wanderer, he faces a past he wants to forget, a present without prospect or fortune, and an uncertain future marred by the loss of his most prized possession – his horse – which he has carelessly gambled away. But he is not without skill – he has an uncanny, if unwelcome, ability to track the most elusive runaway slaves. And to repay a debt and keep his horse, he must head north from Virginia and retrieve a runaway named Rosetta. When he eventually runs Rosetta to ground in Boston, Cain discovers she carries a secret – and the size of the bounty on her head begins to make more sense. Fleeing the northern states pursued by a posse of Unionists, Cain finds himself increasingly drawn to Rosetta and starts to wonder if his five hundred dollar fee – if any fee – could ever be enough to return her to her master…