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 an internship studying dragon languages, and make sure her little sister never has to risk growing up Third Class. By midnight, Viv has started a civil war.

With her parents arrested and her sister missing, all the safety Viv has worked for is collapsing around her. So when a lifeline is offered in the form of a mysterious ‘job’, she grabs it. Arriving at Bletchley Park, Viv discovers that she has been recruited as a codebreaker helping the war effort – if she succeeds, she and her family can all go home again. If she doesn’t, they’ll all die.