Inside every city exist other invisible cities. the Mopa clan live a hidden existence on the rooftops of the huge buildings in the middle of the city. They steal from the supermarket, play in the aisles at midnight and have fun scaring the customers. But their peace is disrupted when trackers of a neighbouring clan disappear with no trace. What has happened to them? Who are the humans that seem to know about them? And most important, what is LAEXHU, the company that's coming after them? Sasa and Film, two young trackers, embark on a dangerous adventure to solve the mystery, but their journey will reveal secrets that will change everything. What is the secret city hiding?