For centuries the intricately carved stones of Rosslyn Chapel near Edinburgh have tantalised historians, archaeologists and devoted Christians. A labyrinth of vaults beneath the 15th-century home of the Knights Templar is reputed to contain dozens of holy relics, including early gospels, the Ark of the Covenant, the fabled Holy Grail - and even the mummified head of Christ. More than 550 years after the first foundation stones were laid, modern technology is about to put the legend to the test. A group of Knights Templar, successors to the warrior monks who sought asylum from the Pope by fleeing to Scotland...