Prodigy by Marie Lu

Day and June have escaped the Republic's confinements, but Day is seriously injured and needs help not only with his injury, but with freeing his younger brother from the Republic's experiments. The only people they can turn to are the Patriots who helped them escape in the first place. Determined to do what they can to fix the madness that is the Republic, Day and June join their forces only to be separated on a mission. Will their relationship survive this test of commitment and is the mission all that it's wracked up to be?