The Lincoln League (Christian Series, Level III)

John Scobell, a former slave, has been treated as an invisible man for all of his life. Now he is a spy for the Union, and he collects secrets in northern Virginia as the Civil War marches down upon the land. But he has no idea that Peg, the wife he left behind in Richmond, has a secret of her own. Peg has also decided to become a Union spy in the heart of the Confederacy, uncovering information about Rebel experiments with submarines that could change the course of the war.