The plot is a very particular series of events with the following labels:  exposition, inciting incident, rising action, climax, falling action, and resolution.  The exposition of the book happens when we learn about Isabel being a slave in the time of the American Revolution.  The inciting incident happens when Ruth, Isabel's sister, is taken away and Curzon is imprisoned.  Isabel vows to find Ruth and help Curzon as Isabel struggles with the ideals of the Loyalists vs. the Patriots.  The rising action is often the largest part of a novel.  This novel is no exception.  There are many events in the rising action that increase the tension in the story.  For example, in the rising action Isabel chooses the rebel side, brings food and supplies to Bridwell prison, and contemplates freedom.  The climax (the height of the tension) happens when Isabel frees Curzon from prison by pushing him in a wheelbarrow past the guard.  The main part of your question, of course, is about the resolution of the story.  The resolution happens when the conflict is resolved and is usually found at the very end.  After the climax of the story, Curzon regains his health and travels with Isabel to find Ruth.  This is most definitely the resolution to Chains.