Spy School Goes Wild by Stuart Gibbs

Ben Ripley is recruited for a top secret mission to bring down his nemesis, Murray Hill, once and for all. But when things go horribly wrong, Ben ends up lost in an extremely dangerous wilderness with Murray—and confronting a new, devious enemy—with none of his friends to help him. Now, Ben must figure out how to survive and deduce what evil plan his new enemy is plotting in time to thwart it.