Prodigy by Marie Lu

 Prodigy picks up where its prequel Legend leaves off. Day and June, who are now refugees from the Republic (which is the western United States), must team up with the Patriots, a rebel group that wants to overthrow the government. In exchange for Day receiving medical treatment and his brother being found, June and Day must help in a plot to assassinate the new Elector. However, when June meets the Elector as part of the plan and realizes that he actually might different than his tyrannical father, she must figure out how to stop the assassination plot and still help Day.
 I really enjoyed the book a lot because the characters were very realistic and I was able to get a good grasp on the plot even though I never read the prequel. My only regret is not reading the prequel beforehand because I would have been able to understand the references made back to it more clearly. Needless to say, though, I will be reading the prequel and the third book, since the ending set the scene for a third book.