In 1361 the troops of the Danish King Valdemar were approaching the city walls of Visby, Gotland. Meanwhile a young girl named Sigrid was frantically laying out clues around the city. Clues that were leading to the whereabouts of a fantastic treasure. She managed to carry out her mission just in time before she was captured and walled up alive in a tower as punishment for not reveling the hiding place of the treasure. Now a 14-year-old Danish girl named Kathrine and her three friends must follow the 700-year-old clues through the wild celebrations of Medieval Week in Visby in order to rescue her kidnapped father and find the long-lost treasure. But the dreaded Black Brotherhood is on their trail. Will the kids succeed in finding Kathrine’s farther and will Sigrid reach forward through time and help them on their quest?