A Killer for the Common Good — Michael E. Cook

As the son of Irish immigrants, young Sean had heard from his parents how the Irish were treated by the British, and how his family would never be slaves or own slaves. In Tennessee, his father taught him how to defend himself and shoot, and how to handle and care for horses. These teachings were of great help at school and at home one night when night riders attacked his family. When his family headed west, Sean had to deal with the massacre of his parents and small wagon train, but his skill with rifle and pistol kept him alive. He learned well from his new family, the Cheyenne, the skills that would keep him alive on the plains. These things would come in handy when dealing with enemies, either man or beast. He loved his life with the Cheyenne, but when the cholera came, his wife and child were taken, and he must go and find himself. Sean becomes good friends with a Sergeant in the Army, and after the war begins, he joins the Union Army. His great skill with his Sharps rifle helps keep him alive during the war. Sean figures that the more he kills, the quicker the war will end. Tragedy strikes again when his unit is in Tennessee, and his childhood sweetheart is raped and murdered by Union deserters. He takes matters into his own hands. When he does this, a former Federal Judge, and now an aide to General Grant, sees Sean potential as a lawman, and asks him to become a Federal Marshal after the war.      Sean does become a Federal Marshal, and his assignments are to get the most wanted criminals by whatever means. There are no judges or courts, few or no jails, and mostly no law where he's headed.