Spy Camp (Spy School Series #2) by Stuart Gibbs

In the second book in the New York Times bestselling Spy School series, top-secret training continues into summer for aspiring spy Ben Ripley-and so does the danger. Ben Ripley is a middle schooler whose school is not exactly average-he's spent the last year training to be a top-level spy and dodging all sorts of associated danger. So now that summer's finally here, Ben would like to have some fun and relax. But that's not going to happen during required spy survival training at a rustic wilderness camp, where Spyder, an enemy spy organization, has infiltrated the spies ranks. Can Ben root out the enemy before it takes him out-for good?