Among the usual blocks of flats on the Sunnyside estate, no one expected the summer to start so unusually. Antek and Kalina, siblings with a passion for adventure and science, were sitting on the roof of their block with a telescope, looking for shooting stars. Their dad said there might be a swarm of meteors that night, so they prepared hot tea and a blanket. Suddenly the sky was cut by a blinding, bright flash. But it was no ordinary meteor - the flash was green and seemed to move strangely slowly. It fell somewhere beyond the forest, beyond the city limits. All around it became as bright as day, and then everything went dark again, as if someone had turned out the light. Kalina glanced at her watch - it had only been two minutes since they had seen the flash. Antek couldn't contain his excitement - "We have to check it out! It could be something cosmic!" The next day, right after their online lessons, they both set off on their bikes towards the forest. The closer they got, the more they felt that something strange was in the air. The sun was shining through the trees, but the light seemed a little greenish. Eventually they reached a small clearing where the grass was scorched into a circle and a metallic object with strange pulsating patterns was stuck in the centre. Suddenly, as they came closer, a quiet sound came from the object, as if someone was whispering a single, unintelligible word. The air trembled and the object opened slowly, revealing an entrance. A green light flashed inside. Antek and Kalina looked at each other, excited and a little frightened. They slowly approached the entrance, and then they heard a loud crack behind them....