Book Group: This month - 'The Da Vinci Code' by Dan Brown

In the Hollywood-style London of The Da Vinci Code, characters vault over turnstiles in Underground stations (not seen for more than a decade) and St James's Park is wreathed in its habitual thick fog. Yet I see Tube travellers deeply immersed in this baffling phenomenon every day. Whatever the source of the New England musician-turned-thriller writer Dan Brown's extraordinary worldwide success, credibility must play a very slender part. With more than 10 million copies in print, and UK sales approaching 1.5 million, Brown's James Bond-ish spin on the quest for the Holy Grail through Paris, Rome, London and Edinburgh has become the Pot Noodle of popular fiction. People devour it guiltily, often ashamed of their addiction. What secret ingredient explains its mesmerising grip? After all, the plot's farrago of fantasy and speculation about the hidden intrigues of the Church and their impact on Western history has filled many other potboilers: notably, Baigent and Leigh

In the Hollywood-style London of The Da Vinci Code, characters vault over turnstiles in Underground stations (not seen for more than a decade) and St James's Park is wreathed in its habitual thick fog. Yet I see Tube travellers deeply immersed in this baffling phenomenon every day. Whatever the source of the New England musician-turned-thriller writer Dan Brown's extraordinary worldwide success, credibility must play a very slender part. With more than 10 million copies in print, and UK sales approaching 1.5 million, Brown's James Bond-ish spin on the quest for the Holy Grail through Paris, Rome, London and Edinburgh has become the Pot Noodle of popular fiction. People devour it guiltily, often ashamed of their addiction. What secret ingredient explains its mesmerising grip? After all, the plot's farrago of fantasy and speculation about the hidden intrigues of the Church and their impact on Western history has filled many other potboilers: notably, Baigent and Leigh's The Holy Blood and the Holy Grail, 20 years ago. If readers know that, at root, it's all a load of old Templars, what keeps them involved? Do far-fetched conspiracy theories that explain the world suit a new cultural climate of dread and powerlessness? Please help us with our inquiries.

'The Da Vinci Code' by Dan Brown (Corgi, £6.99)