Julka, Kuba and Bruno couldn't stop laughing when the Orion rocket suddenly danced through the air as if it wanted to play tag with them. It was their first mission on their own, with no adults, just them and the artificial intelligence Ada, who controlled everything from the course to the automatic cocoa machine. They took off from Earth Station 7, a state-of-the-art spaceport. Around them swarmed other ships, floating cafes and huge screens with news from around the cosmos. But Julka, Kuba and Bruno looked only at each other and at the stars. They knew that in a moment everything would change. Bruno, who always kept a screwdriver in his pocket because it might come in handy (and usually did), was the first to notice a disturbing flickering on the signal panel. "Ada, is this normal?" - he asked, tapping lightly on the screen. "Unknown signal detected. Direction: the moon Ganymede. I suggest caution," Ada replied in a calm, electronic voice. Julka immediately looked at Cuba. A year ago they had read about Ganymede, the largest moon of Jupiter, where an old mine had been established, and now everyone was afraid to fly there because of the mysterious disappearances. "Shall we have a look?" - whispered Cuba with a glint in his eye. "What if it's someone calling for help?" - asked Julka. "Maybe we'll find something in there that no one has discovered yet!" Bruno switched the Orion on course to Ganymede. After a few minutes, as they neared the surface, a blurry image appeared on the screen: a dark blur, as if something huge was standing among the ice rocks. Suddenly, an intermittent voice came from the speaker: "After... po...power... t-there... something is waiting..." Everyone froze. The ship hovered just above the surface of the moon. Inside the cabin it became quieter than ever. And then, out of the darkness, something began to approach their ship.... something strange.