Champion - Legend Series Book 3 - Marie Lu

Champion begins a few months after the ending of Prodigy. Day and June are not together after their break-up at the end of Prodigy, and June still doesn't know that Day is dying. June is one of Anden's Princeps Elect and Day is living with Eden and Lucy, a caretaker assigned to help take care of Eden, as Day is now dying.

The Colonies and the Republic were having peace talks until the Colonies blamed the Republic for a disease that was spreading in their country. The Colonies give the Republic a few days to find the cure for this disease before they start a war. In order to try to find the cure, Anden asks June to request Day's attendance to an emergency banquet, so they can ask Day to use Eden to find the cure.