Confederate Captain Alan Westcott, posing as a horse supplier for the army, is ordered to infiltrate the Union lines and contact William Quantrill to arrange a raid on the arsenal at Lawrence, Kansas. Westcott meets and falls in love with Sue Walters. Westcott's activities and associations begin to cause the Union vigilante committee to become suspicious of him, and he moves quickly in utilizing the Quantrill raiders. After laying their plans to attack Lawrence, Westcott learns that the arsenal is being moved out by wagon trail. He calls off the attack on Lawrence in favor of attacking the wagon train, but Quantrill pulls a treacherous double-cross and rides into Lawrence on a personal mission of bloodshed, murder and looting.