Serena Stark is a farmer's daughter who has never been past the limits of her small town, never seen or done anything remarkable in her life. After the death of her older brother Caleb, she feels as though she is beginning to disappear completely. When Caleb's best friend Sam, who she's secretly loved from afar for years, joins up to fight for the Union in the war, Serena can't bear the thought of losing him as well. One night, in a desperate and rash decision, Serena cuts her hair, dresses in Caleb's old clothes, and strikes off to join up too. Now she is Frank Stark fighting with the Army of the Potomac as it heads for Confederate territory. While she must face peril on the battlefield and the discomforts of army life, her greatest fear is discovery.