Matthias Breecher, a Pinkerton detective and Union Army veteran, is hired by one of the first African-American senators to track down the worst Confederate war criminals. His first mark is General Corbin Dandridge, a former Confederate general he shoots and kills in the general's Mississippi barn.
Breecher then travels west, seeking his next target, Reginald Cooke. Along the way, he crosses paths with bounty hunter Harlan Red, who says they will one day come into conflict. Breecher finds Cooke on his farm and learns that Reginald is being cared for by his daughter Sarah Cooke as he is dying of pneumonia. Breecher decides not to shoot nor hang Cooke, but to stay at his homestead until he passes away from the disease. During his stay, he becomes close to Sarah.
Breecher travels to a neighboring landowner, Fred Quaid. He offers Quaid money to stop threatening the Cookes and get them to sell their land. Quaid challenges Breecher to beat Quaid's best man in a fistfight; Breecher accepts and wins, then returns to the Cooke's homestead. The next day, however, Quaid and several men attack the Cooke homestead. Breecher and Sarah Cooke hold them off. Reginald steps outside with a gun to help, and is shot by Quaid, who is, in turn, shot by Breecher. After building a coffin for Reginald and helping Sarah bury him, Breecher heads west to New Mexico in search of former Confederate Captain Huxley Wainwright.
Staying at a hotel and saloon, Breecher encounters now-Sheriff Huxley Wainwright after a gunfight inside the saloon. Wainwright is suspicious of newcomers, since he stopped receiving letters from Dandridge, and has Breecher waterboarded and knocked out, then instructs two of his men to bury him alive outside of town. Breecher regains consciousness as Wainwright's men are digging his grave and makes his escape, killing both of them. He stumbles to the local church, where he finds saloon bartender Alice Hollenbeck praying, and gives her a message to wire to his patron, Senator Benjamin Burke. She returns with Burke's response that Breecher should use his own discretion and proceed >by any means necessary<.
After giving her a letter addressed to Sarah Cooke, Breecher instructs Alice to hide until the fighting is over and leaves the church. He marches to the saloon and engages in a gunfight with Wainwright's men, which he wins. Wainwright is drawn out, and challenges Breecher to a showdown in which they are both shot. Breecher survives his injury, gives Wainwright's sheriff's badge to Alice, and departs town, later collapsing in a grove.
Harlan Red finds him and bandages his wounds. In thanks, Breecher tells Red where to find Wainwright's body, to collect the bounty. Breecher continues on, eventually reaching the Cooke homestead, where he finds Sarah.
