At the start of the Civil War, Nathaniel Curry is a fifteen-year-old telegraph operator in Richmond. He travels to Washington to see a balloon demonstration and finds himself, entirely by accident, assisting Thaddeus Lowe in directing artillery fire on a Confederate emplacement – the first use of an aircraft in warfare.
A pariah back in Virginia, Nathaniel joins the nascent Union Balloon Corps, the world's first air force. The Corps, a motley collection of adventurers, science enthusiasts and misfits, struggles to find its place within the Union Army. The aeronauts prove valuable, providing information on enemy positions and movements, but are too unruly to be accepted by the military establishment.
Nathaniel, a Southerner, is suspected of being a spy by both sides, even as he has to fight off being recruited as a spy. As the Balloon Corps descends into chaos, even his sweetheart turns against him. Soon his only friend is Abraham Lincoln – and Lincoln wants him to do something that terrifies him.