Galvanized Yankee

In a Northern prisoner-of-war camp during the Civil War, a crippled Yankee commander has a rebellious Rebel executed. The dead man's brother, also a prisoner, vows vengeance. He volunteers to accompany the commander on a mission, planning to murder him along the way but changes his mind and escapes instead, deciding the commander is "already dead." The commander, a changed man, covers up for the escapees and himself faces court martial.