The Always War by Margaret Haddix

At the beginning of the book, a boy named Gideon is at an award ceremony for having killed 1,743 people in a war that has lasted for 75 years. He didn't accept the award because he felt ashamed that he killed that many people. He goes to the enemy's territory to admit that he killed their people, but he ends up finding something very interesting that he never expected. I liked it because it was a page turner and because it was mysterious.