Here is a brief summary of Chains, by Laurie Halse Anderson.
Isabel is a young slave living in the time of the Revolutionary War. She is promised freedom when her owner dies, but instead she and her sister Ruth are purchased by the Locktons, a wealthy and cruel couple living in New York. As she lives through her life as a slave, Isabel meets Curzon, a slave boy, who offers to help her through the Patriots, who are fighting to free the United States from England. The Locktons are secretly Loyalists, pretending to be Patriots so they can continue to live their upper-class lives.
"London? Never!" exclaimed Lockton. "England offers us nothing but taxes, stamps, and bloodshed."
"How odd. Word from Boston is that you still lick the King's boots."
Madam drew in her breath sharply but said nothing.
"Why do you insult me, sir?" Lockton replied.
(Anderson, Chains, Google Books)
Isabel discovers that the Locktons are part of a plan to assassinate George Washington, and turns Mr. Lockton in to the Patriots. He escapes, leaving Mrs. Lockton behind; she becomes increasingly cruel to Isabel, and finally sends Ruth to Charleston. During this time, New York is occupied by the British, who take some of the Patriots prisoner, including Curzon. Isabel helps the movement by sneaking the Patriots food, but is discovered by Mrs. Lockton. Isabel decides to escape and travel to Charleston to find Ruth, but hesitates to leave Curzon behind. Finally, Isabel uses the distraction of the Queen's birthday party to break Curzon out and steal a boat. They row across the Jersey River and Isabel collapses from exhaustion; when she wakes up, she and Curzon are safe and free, ready to go to Charleston and rescue Ruth.
One interesting thing about the book is that each chapter begins with quoted historical material. This allows insight into the norms and customs of the 1700s, as well as allowing the reader to better understand how people thought and acted.