Island CX is a small island on the surface of Zeelich. It is too small to have a settlement, so it is used as a military base instead by the Emperor of Zeelich in Little Big Adventure 2. Its turrets prevent the cabs and other Zeelichian vehicles to land there, while the Emperor himself uses his personal spacecraft to get there from his palace in Otringal.
With nobody returning from Island CX, myths about the island spread, telling about gas monsters haunting the place. Only one franco ever managed to return from Island CX, and is thus able to tell Twinsen about the island's fortress.
Island CX is part of the great rock which has the Island of the Mosquibees at the bottom. There is also a secret passage between both islands in the Village of the Mosquibees. The key to this passage is guarded by Queen Astrid.
When Twinsen comes to the Emerald Moon to save Jerome Baldino, he finds a franco dissident with him. The franco tells Twinsen that the lunar reactors which will set the moon towards Twinsun are controlled from Island CX. The franco is shot during the escape from the Emerald Moon base, and tells Twinsen just before he dies that he must go to Island CX.
Upon arriving on Otringal, Twinsen starts asking many people for information about the island, and in fact spends most of his time in Zeelich searching for it. He eventually manages to find the franco who came back alive from there, at the Island of the Celebration. He tells Twinsen to go see Rick, who in return sends him to talk with Johnny Rocket. Johnny links Twinsen with the dissidents, who instruct Twinsen how to get to Island CX- through the secret passage from the Island of the Mosquibees.
After long adventures all around the planet, Twinsen eventually reaches Island CX throuh the secret passage. He encounters the Emperor, but before Twinsen is able to kill him, the Emperor activates the lunar reactors. Hurried on by Sendell, Twinsen steals the Emperor's Sword, before taking the Emperor's personal spacecraft to the palace at Otringal in order to acquire the last key fragment.