Leon and Maja have always dreamt of travelling into space. When their grandfather, an inventor, invited them to his workshop, they had no idea that on the very first day of their holiday they would embark on the strangest adventure of their lives. In the middle of their grandfather's garden stood a shiny rocket, bigger than their house. Grandpa was smiling mysteriously: "I built it especially for you! Inside there is a research ship waiting for you ready to fly. But remember - anything can happen in space!" A few hours later, with their hearts beating faster than the rocket engines, Leon and Maja were already sitting in the control capsule. Behind the portholes, the stars were twinkling and infinity stretched out in front of them. After several days of travel, the onboard computer issued a warning: "Unidentified planet encountered. Conditions favourable for landing." The children looked after each other with excitement. Upon landing, an extraordinary world appeared to Leon and Mai's eyes. The ground was hot and ruddy, fiery geysers were shooting up everywhere, and there were sparkles in the air similar to flickering skylights. However, the strangest thing was that in the distance, right at the edge of the largest crater, someone had hung a flag on a stick with.... a painted potato. With backpacks full of research tools, Leon and Maja walked closer. There was a quiet rumbling from the crater and the ground trembled slightly under their feet. Near the flag, they noticed footprints - they looked as if they had been left by a three-toed creature wearing size 50 shoes. Suddenly, a strange voice reached them from the depths of the crater. It sounded neither human nor robotic. Maja squeezed Leon's hand, and Leon asked in a whisper: - Do you think someone lives here? A distress signal came from their rocket. The computer called out: "Alien object approaching fast!" The children looked into the darkness of the crater, feeling their hearts beating even faster. Would they dare to go all the way down and see who or what was waiting for them inside the volcanic planet?