The lights of the SOJUZ-17 station's main segment trembled slightly as the Swan transport ship docked at airlock number four. Susanna, Adam and Lena glued their faces to the narrow portholes, trying to see the rings of Saturn hidden behind a coating of yellowish clouds. By now they were really far from anything they knew from Earth. Getting off the ship was a bit like the first day at a new school - goosebumps, with a slight tightness in the stomach. Susanna, the eldest, tried not to let her anxiety show. Adam was excited by every sound, and Lena immediately pulled out her old camera, ready to take pictures of every screw. Already in the lobby they were greeted by Inspector Tarasova, with dishevelled hair, wearing a T-shirt with the station's logo and a fake smile. "I will show you around the laboratories, but remember: don't wander off on your own. Here everything has rules." The station was huge - three main research modules, a hydroponics garden and an observatory equipped with state-of-the-art telescopes. That's where they were heading. On the way, they passed service robots and scientists busy analysing samples from the moons. When they reached the observatory, Lena approached the panoramic window. Saturn seemed unreal - huge, majestic, with rings that glistened in the glow of the distant Sun. Adam found a map of the station on the wall, and Susanna decided to take the opportunity to ask Tarasova a question about the strange radio signals from Enceladus that she had read about in the communiqués. The inspector just shrugged her shoulders. A couple of hours had passed when Lena noticed something disturbing on the observation monitor: a shadow, completely unlike the shadow of moons or rings, was slipping through the image updated every second. Adam tried to move the camera, but the panel suddenly refused to obey, and the lighting in the observatory dimmed. A sound came from the maintenance airlock, as if someone or something was moving in the darkness. Susanna squeezed Lena's hand. "What was that?" - she whispered. Adam was already holding a torch in his hand and moved slowly towards the airlock. He hesitated, looking at the others. "We're going together, aren't we?" They all looked at each other, feeling the tension rise and a distant, unfamiliar echo penetrate the steel walls....