The Dark Land — Jory Sherman

Brad Chambers is a shell of a man. The Confederate Cavalry of the West is disbanded. The South's cause is lost forever. And he's seen too much blood and death for one man's lifetime. All he wants is a reason to go on. 
 
He finds it when his hated nemesis, Abel Thorne, burns a trail of destruction across Texas, slaughtering ex-slaves and wealthy landowners who have bowed to the Union. Chambers has waited years to find Thorne -- the man who caused the destruction of his home and family -- and now the time for vengeance is at hand.
 
But to track down Thorne, he will have to do the unthinkable, and fight alongside his old enemy -- the Union Army...