Chains opens with a funeral, which pretty much tells us up front that it's going to be a pretty bleak story. Isabel, our heroine, and her younger sister, Ruth, are attending the burial of their owner, Miss Mary Finch. The occasion presents a great deal of hope for Isabel and Ruth, as Miss Finch planned to free the girls in her will. When Isabel confronts Miss Finch's brother about this, though, he basically thinks she's making it up.
To make matters worse, her lawyer is stuck in Boston, where a major uprising has just taken place over the British colonies' desire for independence. As a result, Isabel's hopes turn to dust.
We'd like to say that somebody texts the lawyer and he makes an emergency trip to Rhode Island to sort stuff out, but unfortunately (a) that doesn't happen, and (b) it's 1776, so that's impossible anyway.
Instead, Miss Finch's brother sells Isabel and Ruth to Anne and Elihu Lockton, two rich British merchants from New York who are loyal to their country in the independence conflict. They're also not very nice people, especially Anne, who makes the girls call her "Madam" and is basically Mommie Dearest, Cruella DeVille, and the wicked stepmother from Cinderella all rolled into one. Ouch. Sounds like a winner.
As she goes about her duties, Isabel befriends Curzon, a slave who works for Mr. Bellingham, one of the chief law enforcement officials for the Patriots. He tells her that if she hears Lockton, Madam, or any of their Loyalist friends talk about sensitive information related to the conflict, sharing it could likely buy the freedom owed to her and Ruth. Isabel initially rejects his offer, saying that her job is to take care of her sister and she cannot put her sister in jeopardy.
Meanwhile, life at the Locktons' gets pretty difficult for the girls. Madam verbally abuses Isabel and makes Ruth into her personal servant. When Isabel comes into Madam's chamber one day to find Ruth crying, she realizes that they need to get away from the Locktons once and for all. She overhears Lockton and some of his Loyalist friends talking about money they have hidden away in a linen chest to bribe the rebel army with, and Isabel makes a daring, dangerous journey to Bellingham's in the middle of the night to pass the news onto Curzon.
The next day, Patriot officials come to search the Locktons' house. This initially overjoys Isabel, until she learns that Lockton hid the money somewhere else because he figured they'd be stopping by. Lockton is arrested under suspicion of treason, but the powerful influence of his aunt, Lady Seymour, allows him to be set free the next day.
Several days later, Isabel overhears Lockton and his friends plotting to kill General George Washington. She goes to Bellingham's associate, Colonel Regan with the news, and he promises to look into hers and Ruth's case in exchange for the valuable information. Lockton flees to England once he hears that the plot has been discovered.
Ruth is plagued by frequent seizures, which make Madam believe she's demon-possessed. As a result, she sells Ruth after giving Isabel a sedative in a milk beverage to keep her from fighting back. When Isabel learns the truth, she confronts Madam, who has her arrested and branded on her cheek with the letter I for insolence. With two failed attempts at seeking help from the Patriots and her sister now long gone, Isabel feels more hopeless than ever.
Curzon comes to see Isabel and tells her how sorry he is that things didn't work out. He explains that Bellingham has asked him to take his place and fight on the American side in the war. Isabel also hears rumors that the British intend to free any slaves who will run away and support them, so she decides to give this a try and heads to a British ship when Madam sends her to run errands. Unfortunately, no one will accept her help. She does, however, experience a welcome break when Lockton farms her out to help Lady Seymour, who is in poor health.
Things get worse when New York City literally catches on fire and the blaze destroys a giant chunk of the city. Isabel rescues Lady Seymour from her burning house, and the two of them develop a friendship after Isabel saves her life. They return to the Locktons' home, where much of Isabel's duties consist of caring for Lady Seymour, who becomes debilitated after the horror of the fire.
When the British capture Fort Washington, all the Patriot troops are thrown in the British prison not far from the pump where Isabel gets the Locktons' water. Isabel learns that Curzon is among them, and begins bringing leftover food to the prison. When she sees that the other soldiers are mistreating him because he is a slave, she makes a deal to deliver messages to their captain, who is out on parole in the city. Isabel thought her spy days were behind her, but she can't just let her friend die.
Isabel's double life as a slave and Patriot spy gets majorly disrupted when Madam learns of her activities. In her string of verbal abuse, Madam lets it slip that she actually still owns Ruth—because she couldn't find a buyer for her, Ruth was sent to the Lockton estate in Charleston. Isabel is understandably pretty upset about this, so Madam locks Isabel in a potato bin and threatens to have Ruth drowned as a punishment for helping the Patriots.
Knowing that Ruth is still in the Colonies gives Isabel the courage to bust out of the Locktons' house. She steals a pass from Lockton that declares that she is a free slave, gives herself a new name, and leaves.
She is about to steal a boat and row across the river to New Jersey when she remembers how kind Curzon has always been to her, and knowing that she can't leave him behind, she goes to the prison and pretends to be cleaning cells. She finds Curzon lying on the floor, delirious with fever, and tells the guard that he's dead. When he gives her permission for her to take him to the pile of bodies outside, she puts him in a wheelbarrow and takes off for the dock.
Curzon and Isabel get a boat and row like mad across the river before collapsing unconscious on the New Jersey banks. When she realizes she's gotten the two of them out of New York to safety, she asks Curzon if he's able to get up and walk… and the story continues in Forge, the next book in the series.