A warm June evening was spilling soft light over Silver Lake. The smell of pine trees was in the air and the first stars were reflected on the water. Sitting on the shore were Lena, Bartek and Ignacy. They had been friends since childhood, and these nightly gatherings under the open sky were their own ritual for the end of the school year. That evening, they did not talk about exams, holiday plans or everyday problems. Bartek - always a bit thoughtful and intrigued by the world - took out an old notebook from his backpack, recently found in his grandmother's attic. The leather binding was cracked, the pages smelled of dust and memories. A faded inscription on the cover read: "Warning: for insiders only." - Perhaps it was an old diary or journal of some kind? - Lena tried to look over Bartek's shoulder. Bartek, already sensing adventure, opened the notebook. Instead of the usual notes, on the first page they saw an elaborate drawing showing the area around the lake and inscribed somewhere between the trees, strange symbols. Next to them was a laconic note: "Shadow over Silver. Begins when dusk falls. Look for traces under the old oak tree." Ignatius, who was usually sceptical of such stories, fell silent this time. Something about the words - perhaps the way someone had written them, perhaps the mysterious announcement itself - made them feel a thrill of excitement. For a moment neither of them moved. Finally, Lena rose and looked towards the woods, where the dark shape of an old oak tree could be seen. - Let's check it out. What's the harm? Holding the torches and notepad, they walked between the trees. As they approached the oak tree, the night grew thicker and thicker and the silence around them became more and more unnatural. And then, just under the roots of the tree, Bartek spotted something metallic glinting in the torchlight. They pulled out an inconspicuous, rusty box. When Lena tried to open it, an icy wind suddenly blew, even though the air had been calm only moments before. A shrill scream rang out in the distance, and a figure, whose outline they could not recognise in the gloom, ran out of the depths of the forest....