Legend takes the form of interwoven first-person narratives. One voice is that of Day, a 15-year-old boy from the slums who is the most wanted criminal of the Republic. The other voice is June, a 15-year-old girl from a privileged class, training in the most prestigious military academy for the Republic. The author's bio on the book jacket notes that the impetus of this story came from Lu's watching Les Misérables and "wondering how the relationship between a famous criminal and a prodigious detective might translate to a more modern story." Day is the criminal with a heart of gold, then, though his character also becomes a bit of a renegade saboteur, working to undermine the Republic's regime more than simply stealing to help out his family. June is the righteous arm of the law, but instead of questioning her own worth as a person and her own ideals, she begins to see how the Republic is not all she was brought up to believe it is.
The post-apocalyptic world Lu creates is fascinating. It is set in a future where the United States has become fractured into different warring polities, where flooding and a changed climate have reshaped the landscape dramatically. The novel is set in a Los Angeles where many of the high rises are flooded up to the fifth floor or more. One of the things that this first novel in the series does well is set up a lot of questions about this world. It's set in the future, but how much is our own present world supposed to be the past for this future? What happened to split the country up? What are the allegiances between the different polities (the Republic and the Colonies are the two major ones, it seems, though there may be others)?
The novel is ultimately very much about the encounters between Day and June and what they ultimately learn about and from each other. Both are prodigies (the title of the followup book, incidentally, is Prodigy), extremely gifted youth in their mental, physical, and deductive faculties. What is fascinating is the way they are set up as parallel characters, equally outstanding but with entirely different life circumstances. In this way, there is a pointed commentary about how social factors influence the expression of more innate abilities.
The Republic is an authoritarian state that presents itself as a benevolent meritocracy. All citizens take the Trial at the age of 10, and if they pass, they get assigned to particular jobs in the Republic based on their scores. If they fail, they get sent to labor camps, which June discovers during the course of the novel are not what they seem.
The general trajectory of the plot is the hunt of Day by June. The novel begins with Day's infiltration of a hospital to steal a cure for the plague that has afflicted his younger brother Eden. Through a series of events, June becomes the lead agent in the quest to bring in the Republic's most dangerous criminal, and how she goes about finding Day is particularly fascinating. One of the central issues in the novel is the presence of plagues that pop up in different sectors of the city every year. The Republic deals with the plague in very ruthless ways, quarantining families and taking the sick away. Of course, the wealthy get yearly vaccines that prevent them from getting sick, so it is only the poor neighborhoods that suffer from this illness.
There are a few hints of the importance of race in this post-apocalyptic world such as mention that the Republic has conquered China, either by wiping it out or subjugating it as a business market (the mythical idea in business of taking over the consumer market of such a vast country). And Day is listed as predominantly "Mongolian" in his files, despite his bright blond hair and blue eyes. The use of an outdated racial term, Mongolian, is also interesting in its reference to a scientific worldview that is more willing to assign values to different groups of people based on physical characteristics (and implied psychological or mental characteristics).