Dakota Territory, 1866. Following the murders of a frontier fort's politically-connected provisioner and his wife in their illicit off-post brothel, Lieutenant Martin Molloy and his long-suffering orderly, Corporal Daniel Kohn, are ordered to track down the killers and return with "boots for the gallows" to appease powerful figures in Washington. The men journey west to the distant outpost in a beautiful valley, where the soldiers inside the fort prove to be violently opposed to their investigations. Meanwhile, Irish immigrant brothers Michael and Thomas O'Driscoll have returned from the brutal front lines of the Civil War. Unable to adapt to life as migrant farm laborers in peacetime Ohio, they re-enlist in the army and are shipped to Fort Phil Kearny in the heart of the Powder River Valley. Here they are thrown into merciless combat with Red Cloud's coalition of Native tribes fighting American expansion into their hunting grounds. Amidst the daily carnage, Thomas finds a love that will lead to a moment of violence as brutal as any they have witnessed in battle -- a moment that will change their lives forever.