The real mystery lurking in the chapel where Dan Brown set The Da Vinci Code. From the outside, the Rosslyn Chapel does not look like a suitable place to hide Jesus' head. It's not much bigger than a country church, standing inconspicuously on a small hill in the miniature Scottish town of Roslin, a few miles south of Edinburgh. Its Gothic pinnacles, flying buttresses, and pointed arches have been battered by 500 years of capricious weather, and for years it has been encased in an exoskeleton of scaffolding as restoration efforts plod along. Until recently, it was covered by a...