Freedom

The people in the Castle of the Red Tower do not have a will of their own because of caps, machines that constrict thoughts which are controlled by huge, three legged machines called Tripods. No matter how friendly they seem, they are controlled by the Tripods, and thus, they are the enemy of Will, Henry, Beanpole and all the other rebels. Will will do anything to avoid being capped, and to get to the White Mountains, but he has feelings for Eloise, so he discovers that freedom comes at a price.