Carmen and Juni Cortez are now full-fledged agents of the OSS, following in their parents' footsteps. Their latest mission begins at a high-tech amusement park where they thwart an evil plot but soon find themselves facing their biggest challenge yet. The President's daughter accidentally loses control of a top-secret device known as the Transmooker, which has the power to disable all electronic devices, making it a highly coveted asset. Carmen and Juni must recover the Transmooker before it falls into the wrong hands. However, they are not alone; a rival spy duo, Gary and Gerti Giggles, also seek the device, leading to a fierce competition between the two pairs of young spies.

Their journey takes them to a mysterious island that doesn't appear on any map. This island is inhabited by strange creatures and governed by the scientist Romero, who has renounced his former evil ways. The siblings must navigate the island's many perils, including bizarre animal hybrids and natural traps, all while outsmarting the Giggles siblings. As they delve deeper into the island's secrets, they encounter numerous obstacles that test their ingenuity, teamwork, and bravery. Concurrently, their parents, Gregorio and Ingrid Cortez, are facing their own set of complications, urging them to come to their children's aid. Their quest for the Transmooker uncovers hidden truths and leads to revelations that redefine the scope of their mission.