The conclusion of the Secret Coders series. And a nice conclusion it is too.

The coders, Hopper, Eni and Josh, have to travel to Professor Bee's place of origin, Flatland, to obtain an object which will help them to defeat One-Zero. That they do, learning a bit about Flatland while doing so. With the object in their possession, they return and, with some coding, come up with a scheme to defeat One-Zero's plans to take control of their city and make everybody 'happy'.

In the course of the book, the coders learn about multiple-loops and subroutines and how to incorporate them into multiple main programs, which are needed to defeat One-Zero. But it would also require some quick non-coding thinking on the coders' part to finally rid the world of One-Zero.