There are many dramatic and exciting scenes in Laurie Halse Anderson's Chains. However, to be pivotal, a scene must not only be dramatic in itself, but must affect the rest of the action in the novel. In other words, something essential, or several important things, must "turn" on the events described. The scene in which Isabel is branded with the letter I by Anne Lockton is an example of an event that is important and memorable but not pivotal.
The most pivotal scene in the book, therefore, is the one in which Isabel makes a bargain with Curzon that she will spy on the Locktons in exchange for a chance of freedom. The Locktons are Loyalists, which is to say they are loyal to the British crown. This scene sets in motion a chain of events that have important repercussions for Isabel, Curzon, the Locktons, and American society as a whole. This is because Elihu Lockton has been conspiring to assassinate George Washington, a conspiracy that is discovered and frustrated by Isabel. This scene, therefore, is pivotal because what happens in it not only leads to the freedom of Isabel and Curzon and forces Elihu Lockton to flee the country, but also shapes the course of American history.