Volume 3 in the mind-bending new series from Gene Luen Yang! Hopper never dreamed that there was a connection between the Bee School and her missing father -- but it turns out that Albert Gracie was also a student of this mysterious coding school. His disappearance can only be the work of Dr. One-Zero. Once a star pupil of the Bee School, Dr. One-Zero is now a green-skinned villain on the hunt for "the most powerful turtle in the world." And the coders...

Dr. One-Zero won't stop until the whole town--no, the whole world--embraces the "true happiness" found in his poisonous potion, Green Pop. And now that he has the Turtle of Light, he's virtually unstoppable. There's one weapon that can defeat him: another Turtle of Light. Unfortunately, they can only be found in another dimension! To open a portal to this new world, Hopper, Eni, and Josh's coding skills will be put to the test.

The Coders uncover a clue that may lead them to Hopper's missing dad, but they may need to use Professor Bee's Turtle of Light to find him.