The Middle Ages were a time of wonder. They gave us the first universities, the first eyeglasses and the first mechanical clocks as medieval thinkers sought to understand the world around them, from the passing of the seasons to the stars in the sky. In this book, we walk the path of medieval science with a real-life guide, a fourteenth-century monk named John of Westwyk - inventor, astrologer, crusader - who was educated in England's grandest monastery and exiled to a clifftop priory. Following the traces of his life, we learn to see the natural world through Brother John's eyes: navigating by the stars, multiplying Roman numerals, curing disease and telling the time with an astrolabe. We travel the length and breadth of England, from Saint Albans to Tynemouth, and venture far beyond the shores of Britain. On our way, we encounter a remarkable cast of characters.