Overview: The team are on the trail of a medieval mystery. Founded by Henry V and built by his son Henry VI, Syon Abbey was a large, wealthy monastery for nuns of an obscure Swedish order. During the reign of Henry VIII it vanished. Its remains lie beneath the lawns of modern Syon House, designed by Capability Brown. What they find is on a huge scale. But there is disagreement as to what kind of building it was. After investigating the foundations of the House, Stewart and Jonathan reach an agreement on the extent of the church. They are joined by buildings historian Jonathan Foyle and monastic expert Barney Sloane.