Dan Brown's novel The Da Vinci Code claims to be built on real history: real art, real architecture, real secret societies. Tony Robinson tests that claim against the record, tracking the book's central assertions about the Holy Grail through churches, art galleries, and archives, and putting them to historians rather than novelists. He examines whether the Catholic Church suppressed the truth about the Grail, whether secret societies have guarded it for centuries, and whether Leonardo encoded its secret into The Last Supper, the painting Brown leans on hardest. Robinson treats himself as a skeptical investigator rather than a believer, checking each claim against what scholars actually know about the Grail legend's origins and asking where Brown's sources come from. The film's real question is whether the men Brown drew on, and the Grail hunters before them, were reporting fact or constructing an elaborate hoax that a bestseller then mistook for research. It ends closer to the historians' skepticism than to the novel's certainty.