Cody wasn't looking for trouble. He was just looking for a library book on competitive snail racing. But when a boring gray book falls off the shelf, a mysterious card tumbles out a card with a strange symbol and a coded message: The hamster needs a new cage. Before he can even finish his homework, Cody is accidentally recruited into The Treehouse, a top-secret spy agency hidden right under his nose. As their newest agent, "Badger," his life is suddenly filled with juice-box debriefings, cafeteria stakeouts, and a grumpy handler named Agent Sparrow. His missions? Decoding secret messages from lunch ladies and using high-tech gadgets disguised as school supplies. But just as Cody starts to learn the ropes, he's cornered by the other side.

The mysterious and smooth Ms. Vex, leader of the rival Shadow Syndicate, makes him an offer he can't refuse: become a double agent. All he has to do is spy on The Treehouse for her... and he'll get paid in high-end Swiss truffles. Now, Cody is trapped. He's officially The Youngest Double Agent. He's juggling two sets of invisible inks, lying to his best friend Maya, and trying to keep his two secret identities from colliding. When a priceless, high-tech drone becomes the centerpiece of the school Science Fair, both agencies will do anything to get it. Caught between two masters and a school-wide conspiracy that goes all the way to the principal's office, Cody must use his wits, his grappling-hook backpack, and his best friend's help to unmask a secret mole... and decide who he's really spying for.