In the heart of the Emerald Forest, where the paths disappeared under the soft moss and the morning mists floated lazily over the treetops, three friends - Lena, Antek and Maks - met every week for explorations together. They each had their own talents: Lena understood bird speech, Antek excelled at tracking tracks and Maks knew all the plants like the back of his hand. This time, however, their adventure was to be different. For several days, the animals in the forest had been behaving exceptionally strangely. Squirrels had been disappearing for hours, deer had been hiding in the densest bushes and owls had been hooting alarmingly even before sunset. But something else bothered them most - just after dark, a metallic, repetitive sound came from deep in the forest. It resembled an echoing clatter, as if someone was playing a hidden instrument. "Maybe it's just the wind," muttered Maks, but no one believed him. That day, they decided to go deeper than ever before. They took torches, notebooks and old night vision goggles that Antek had got from his grandfather. The more they went into the thicket, the stranger things they saw. Trees bent into unnatural shapes, paw prints they couldn't recognise, and even abandoned bird nests. Suddenly, a large black raven emerged from the foliage right next to them and left a feather of a light green hue under their feet. "That's impossible... Raven feathers are never green," Lena whispered and bent down to pick it up. At the same moment, the same mysterious sound rang out - louder than ever before. The friends looked at each other, knowing that they could no longer turn back. They moved towards the source of the sound, unaware of what awaited them between the mysteriously broken trees. And then, as they stood in a clearing hidden among the thicket, they saw something that changed their view of the Emerald Forest forever....