Paperback bestsellers/mass market.

How hot is Anchor's mass market edition of The Da Vinci Code? Consider these numbers: for the week ending April 15, the top three chains (B&N, Borders and Walden) sold 33,405 copies of Brown's juggernaut, while the second-place titles racked up combined sales of 10,056. For the mathematically challenged, that's triple the difference.

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Brown began researching his 1998 novel while teaching at Phillips Exeter Academy, when a student was flagged by the Secret Service as a national security threat based on a comment he made in an e-mail. Brown learned about an intelligence agency known as the NSA (jokingly referred to as No Such Agency) that …