Zosia adjusted her thick suit and looked out of the panoramic window of the Gaia orbital station. From this height, the Earth looked like a blue-green sphere, surrounded by delicate streaks of clouds. The station was bigger than she could have imagined - it had hundreds of corridors, secret doors and quiet nooks and crannies that none of the students had yet managed to explore. This summer, Zosia, her little brother Nikolai and their friend Amir had the unique opportunity to participate in the Space Explorers programme. Every day they learned new things: how to control a droid, how to grow plants in weightlessness and even how to recognise meteorite marks on the station's plating. However, something strange began to happen. First there were quiet murmurs at night, when the whole station should have been asleep. Then some doors in the technical section started to open and close by themselves. The most disturbing thing, however, was what happened this morning. During his usual activities, Nikolai found a strange-looking symbol on the wall of the cabin, resembling a cross between constellations and digital signs. It was carved deeply, as if someone had deliberately hidden a message. Zosia took a picture of it and started looking for similar signs with Amir. The boy was fascinated by codes and ciphers - he immediately tried to decipher the mysterious inscription. During the night, the three friends slipped out of the bedroom. The door to the technical section was unlocked and they could feel strange vibrations inside. As they walked through the semi-darkness, their eyes widened - in the centre of the small room floated a glowing sphere, with digital numbers and flickering lines swirling around it. It seemed to pulsate, as if it had a life rhythm of its own. Suddenly, the sphere shone with a blinding light, and an electronic whisper sounded around it: "Twenty-four hours left until activation...". The children looked at each other, clustering in a tight circle. What did this strange message mean? Was the station in danger? And who or what wanted to give them this mysterious message?