A copperhead is a turncoat - a northerner who sympathises with the South. Captain Nate Starbuck, forced out of his beloved Legion by the enmity of its founder, General Washington Faulconer, becomes caught up in a dangerous double game of espionage. He is given no choice but to travel from a prison cell in Richmond, Virginia, to the secret centre of the high Northern command in a desperate attempt to thwart Yankee strategy which threatens to overwhelm the South.