Take a sacred treasure. Add a secret conspiracy. Attach a name well known to scholars — Dante, Poe, Wordsworth, Archimedes, Machiavelli, Shakespeare, the Romanovs, Vlad the Impaler, "Hypnerotomachia Poliphili," whatever — and work it into a story that can accommodate both the Glock and the Holy Grail. If there's any room left for the Knights Templar or DNA samples from Biblical figures, by all means plug them in.The NY Times talks about Dan Brown and the many cloned spin-offs that call themselves books.
Thanks, Dan Brown. Look what you started...
The Da Vinci Clones
From the NY Times: