London, 1923. Dragons soar through the skies, and protests erupt on the streets, but Vivien Featherswallow isn't worried. She's going to follow the rules, get a summer internship studying dragon languages, be smart, be sweet, and make sure her little sister never, ever has to risk growing up Third Class. She just has to free one dragon. By midnight, Viv has started a civil war. With her parents and cousin arrested and her sister missing, Viv is brought up to Bletchley Park as a codebreaker--if she succeeds, she and her family can all go home again. If she doesn't, they'll all die. As Viv begins to discover the secrets of a hidden dragon language, she realizes that the fragile peace treaty that holds human and dragon societies together is corrupt, and the dangeroous work Viv is doing could be the thread that unravels it.