Six months ago, the forces of Thule swarmed across the country's borders, determined to recapture the glory of the Old Empire. Along they way, they are conquering the outlying territories which have been independent since it fell centuries ago. With airships and giant landcruisers, the Thule have quickly overwhelmed smaller nations, including the kingdom of Poziel.

The people of Poziel's last line of defense is their only remaining armored train, Ironheart, a rolling fortress on the tracks. She and her crew stand between the Thule and complete conquest of the nation. Taryn Eile, a young woman fresh off the farm, is attached to the armored train as part of a squad of skirmishers. In the crucible of the war, Taryn sets out to prove herself. As the Poziel army reels from defeat after defeat, she and her squadmates begin to question their own beliefs and their faith.