Tim Sutherland and the team make a return trip to Sweden, where they hunt for clues to a battle that took place on the island of Gotland. Having discovered a pit of crossbow bows in the neighbouring village of Mästerby, they believe below lies the secrets of a forgotten battle. This is the incredible story of the defenders of Mästerby. Leading Swedish archaeologist Maria Lyngstrom joins Tim and Simon in their quest to uncover the secrets of one of the Middle Ages' most elusive battles.