Nurse Mercy Lynch is recently widowed, but the war has further unpleasant surprises in store. While working in a Confederate hospital, she receives word that her estranged father is dying and wants to see her. But reaching the far side of the country will be a harrowing adventure though war-torn border states. When her dirigible is shot out of the sky, Mercy is forced to join the mighty Union-operated steam engine known as the Dreadnought. But the journey turns deadly when they are beset by bandits, then attacked by Rebel soldiers. The train is moving away from the battle front, so Mercy can't imagine why they're so interested. Unless the train's mysterious cargo is responsible? Mercy just wants to see her father before he dies. But she'll have to survive Union intrigue and Confederate opposition to make it off the Dreadnought alive.