A seemingly ordinary sky had stretched over the town of Unai for centuries, but only a few people knew that it took on a delicate purple hue after dark. Sara, Michal and Lena had been inseparable friends for years. Their daily life flowed to the rhythm of tedious lectures, mist-shrouded morning coffees and evening conversations by the alleys of the old park. It was there, among the meandering paths and mossy benches, that Lena noticed something that forever broke them out of the patterns of everyday life. Under one of the twisted trunks of a huge oak tree lay a thin, silvery thread - as if someone had ripped open a patch of sky and hidden it underground. When Sarah tried to pick it up, she felt a gentle tingling under her fingers. Michal joked that it was probably a signal from an alien civilisation, although he visibly tried to hide his anxiety. The next day they returned there, already in the dark, with torches and a huge cup of courage. They were surprised to find that not only had the thread not disappeared, but it seemed to have expanded - it lay spread out among the roots, pulsating with pale light. Lena, the first to do so, slipped her hand between the roots, and her hand... fell inside, as if plunging into the warm current of the river. Sara froze, and Michal pulled out his smartphone to record, though his hands were trembling. After a moment, Lena released an oval, ice-cold stone from her hand. The boy touched it, and then a whisper like the rumbling of a waterfall suddenly spread around them. Everything began to blur - the torchlight ran deep into the trunk instead of ahead. The air thickened and suddenly they heard the sound of something that could not have happened on this side of the tree. Luminous footsteps appeared next to their feet, leading towards an open gap under the tree. The footsteps flared stronger with each passing second, as if something or someone was inviting them inside. Sara looked anxiously at her friends. A decision hung in the air. Should they step over the threshold and see where the glowing path led? As Lena carefully placed her hand on the trembling stone, the whole clearing trembled and the fissure opened wider, revealing a fragment of a completely different world - indistinct, jittery, full of colours and sounds they had never heard. Before they could make up their minds, a whisper they didn't understand rang out from behind them, and a shadow flashed through the darkness. Then everything around them swirled, and a space opened up beneath their feet that invited them to enter....