Lassiter 1: High Lonesome

Lassiter rode into a mess for $250. He was to kill a man that had killed his employer's brother.
When he rode into the town of McDade, he found himself in the middle of a civil war. Two old war officers, a Yankee who hated the Confederacy and a Rebel who loved the South were vying for control of the territory. Lassiter had been in town for four hours, been braced by the Sheriff, offered a job by the Rebel, and when he tried to ride out of town, had to kill the Sheriff and his deputy.
Now he's the Sheriff and charged, for a piece of the action, with getting rid of the Yankee and his pet gunman, a black gunfighter, who had already killed the man Lassiter had come to town looking for.
But, as usual, Lassiter has his own agenda.