The wind wheezed between the sharp rocks of the fjord and the waves crashed against the shore with a bang. On a high cliff, at the edge of a huge forest, stretched the small village of Hammarstad. Wooden houses, covered in a thick layer of moss and turf, clung together as if protected from the fury of the northern sea. It was here that Liv, Ivar and Olle lived - three teenage Vikings who shared a love of adventure, jokes and spinning stories around the campfire. As the sun was just beginning to spill its golden glow over the snow caps of the mountains, the whole village was preparing to go cod fishing. Liv, however, slipped off in a completely different direction, with a canvas bag slung over her shoulder. Already waiting for her there were Ivar, a strong but always slightly thoughtful boy, and Olle, whose agility and quick thinking had often saved them from trouble. - Are you all ready? - whispered Liv, raising her eyebrows in a questioning gesture. - Sure! - replied Ivar with enthusiasm. - If what Grandpa said is true, this cave really does hide something extraordinary. Grandpa Olle had often told stories about an ancient cave hidden deep beneath a rocky slope, where it was said that during storms the sky would light up with a strange light. Although many adults considered these tales to be mere legends, the three friends could not resist the temptation to test their veracity. Several hours of climbing and trudging through dense bushes led them to the entrance - a dark crevice right next to a waterfall. Above it was carved the symbol of a hammer, barely visible from under the lichen. Liv pulled out a seal fat lantern and, clutching it tightly in her hand, entered first. There was a chill in the air and a strange echo, as if the cave walls were memorising every step. The further they descended into the depths, the more they felt the tension building up. At last they reached a wide chamber. In its centre, on a stone pedestal, rested an object resembling a hammer - massive and covered with runes. As Liv approached and held out her hand, a blue flash suddenly pierced the air, and an echo of thunder carried across the rocks. The friends looked after each other with wide-open eyes. The stone walls began to tremble, and somewhere in the depths of the cave there was a sound like a distant chorus. Something that had hitherto slept in silence for centuries had just awoken....