Behind the high, snow-covered mountains, on the shore of a wide fjord, lay a Viking village. Strong warriors lived there, but also children - like Ivar and his older sister Freja. Ivar was seven years old and very curious, and Freja, although nine years old, was never afraid of adventure. One morning, while the dew was still glistening on the grass, the children woke up to hear something unusual. On the other side of the fjord, deep in the dense forest, there was a sound they had never heard. It was not the cry of a wolf or the singing of birds, but something that resembled the long, loud sound of a horn. - 'Did you hear that, Freja? - Ivar asked, looking towards the darkening trees. - 'I heard it, Ivar. Maybe someone out there needs help! - replied her sister. Mum had let them play close to home, but on this day curiosity was stronger. They grabbed thick coats and warm hats and set off quietly across the log bridge until they came to a forest path. The forest was full of shadows and rustling leaves. Ravens cawed over their heads and pinecones fell on the snow with a clatter. Ivar squeezed Freja's hand tightly. Suddenly there was the sound of a horn again. It was closer than before. Behind a bush of wild berries they spotted something shiny. It looked like a small, silvery horn, stuck into the trunk of an old oak tree. Next to it, there were strange footprints in the snow - they didn't look like wolf or moose paws. They were ... round and kind of snake-like. Freja looked at her brother with wide eyes: - Ivar, what could this be? Did someone leave this horn here? What if it comes back? At that very moment, the snow snapped right behind them. Ivar felt someone lightly touch his shoulder....