Thirteen-year-old Isabel Finch was promised freedom upon the death of her mistress. But when she dies, the mistress’s greedy nephew sells Isabel and her 5-year-old “simple-minded” sister, Ruth. The girls become the property of Mr. and Madam Lockton, New Yorkers who stand with England in the impending Revolution. Isabel meets a slave boy named Curzon who convinces her she can earn her freedom by spying for the Patriot forces.
Madam Lockton, a wealthy and self-absorbed Loyalist, dislikes Isabel and renames her “Sal.” When Madam witnesses one of Ruth’s epileptic fits, she’s convinced the girl is possessed. She eventually sells Ruth behind Isabel’s back. Isabel pleads for assistance from Patriots she’s been aiding, but they do nothing to help find her sister. Instead, they allow her to be punished for disobeying her mistress. Isabel has an “I for Insolence” branded on her cheek, and she is dragged through the streets behind a horse cart. After losing her sister and suffering so much physical pain, Isabel grows depressed and hopeless. She becomes convinced that neither the Loyalists nor the Patriots will help slaves like herself.
As the American Revolution begins, British forces lodge in the homes of Loyalists, including the Locktons. A massive fire engulfs the city, destroying hundreds of homes, shops and churches. Isabel saves Lady Seymour, Mr. Lockton’s aunt, and serves as a nurse for the old woman. When Isabel learns Curzon has been imprisoned while fighting with the Patriots, she secretly begins bringing him and his fellow soldiers food scraps. The Patriot prisoners are sick and hungry with few blankets to go around. Madam is furious when she learns of Isabel’s trips to the prison, but Lady Seymour covers for Isabel by saying the visits were her idea as an act of Christian charity. When Madam catches Isabel passing messages for the Patriot commanders, Isabel flees. She rescues the ailing Curzon from prison, gets a small boat and rows them out of New York to Jersey in search of Ruth. The story continues in the next book, Forge.