To help bring the war to an end, Union officer Maj. Lex Kearney (Gary Cooper) volunteers to go undercover and infiltrate a rebel band of horse thieves. But to do this, he must pose as a dishonored soldier, discharged for cowardice and ties to the South. Unable to share the truth of his humiliation, Kearney eventually gains the trust of the rustlers and exposes a tapestry of Confederate as well as Union greed and deceit in the process.