In the Orbit-5 colony, suspended between Saturn's rings, everything was different from Earth. Pupils flew to lessons in rocket boots, and the school canteen served energy jellies instead of potatoes. But most interesting were the programming lessons - each class had its own fleet of drones for experiments and races. Len, Ada and Tilo - three friends from fifth grade - were unofficially the fastest in the drone races. One morning, as they entered the computer room, Len stopped abruptly. "Where are our drones?" he asked in disbelief. Ada looked around the empty table. Apart from a few repair parts, there was not a trace left of the drones. Tilo looked at the marks on the floor - small, as if someone had dragged something heavy. "Maybe someone is making a joke?" he suggested, but Ada was already reviewing the data from the service terminal. "The last movement was registered at 03:17 - the security systems did not detect anything." During the break, they talked about the strange situation. Several students from other classes also complained about the absence of several drones. The robotic cleaner assured that he had seen nothing unusual, but his electronic eye blinked a little too often. In the evening, as the whole school was getting ready for night mode, Len suggested: "Let's hide in the lab and see what happens after dark." They slipped in through a side door. Ada spread out a blanket next to the server room, while Tilo armed himself with an ultraviolet torch and a self-programmed motion detector. The clock was showing 03:15 when suddenly the whole corridor went dark for a moment. They heard a soft clanking, as if something was sliding just outside their door. Til's detector flashed red. Three shadows, unnaturally agile, flashed across the ceiling towards the locked storage room. Len's heart beat faster. "They can't be students..." he whispered. The door to the storeroom opened silently and the shadows disappeared inside. The friends looked after each other and - keeping close - moved to follow the unexpected visitors. Inside, they saw something they had never expected....