After the film adaptation of The Da Vinci Code grossed more than $750m worldwide, Dan Brown could have been forgiven for letting his thoughts drift to Hollywood when he sat down to write this third book in his Robert Langdon trilogy. The Lost Symbol flits constantly between scenes long-beloved of action film audiences, from a car speeding from an exploding laboratory to a helicopter chase across the American capital. The novel's ceaseless activity (its events are squeezed into a single evening, with the protagonist nearly always on the run) keeps the pages turning. But the pyrotechnics are a valiant effort to add colour to what is a fundamentally unsatisfying read, hamstrung by flimsy plot structure and a wearisome preoccupation with New Age pseudoscience.

The book broadly follows the formula used to such lucrative effect in Angels And Demons and The Da Vinci Code, which delighted conspiracy theorists with portrayals of secretive religious societies such as the Illuminati and Opus Dei. This time Brown takes on the enigmatic organisation of Freemasonry, as Robert Langdon races to save a friend from a ruthless figure – known only as Mal'akh – who is driven to kill by his desire for the most potent of the Masons' ancient secrets.

Age-old rumours of a vast Masonic pyramid beneath Washington DC see the action centre on the American capital, and the Harvard symbologist hero takes in some of the city's most venerable landmarks as he follows a seemingly interminable treasure trail of ancient puzzles. In tow is Katherine Solomon, the sister of Langdon's captive friend, whose tragic family history hints at an appalling trauma behind the villain's quest for enlightenment. Further drama is provided by a sinister CIA delegation, with dark warnings that Langdon's mission is of the utmost national importance.

Few come to Brown for stylistic brilliance, and he shows no sign of having refined his literary touch since Stephen Fry wrote off his fiction as "arse gravy of the worst kind". Far too often, he uses his characters as mouthpieces for tedious gobbets of historical and religious trivia, blowing any hope of convincing dialogue out of the water. Thus we have a burly security guard with a buzzcut breathlessly intoning: "Apotheosis means 'to become God'? I had no idea."

Brown's attempts to enliven proceedings by peppering the text with italicised interjections like "Holy shit!" and "There's more?" are redundant outside a comic strip. And there's no excuse for his habit of setting the scene using entire paragraphs that might have been lifted from an official Washington tourist guide. Surely Brown can think of snappier openings to a pivotal chapter than "Washington National Cathedral is the sixth-largest cathedral in the world"?

Such clunking prose would be more bearable if it delivered a ripping yarn of the order of The Da Vinci Code, which broke sales records worldwide by exploring the tantalising, if improbable, notion that Jesus fathered children with Mary Magdalen. But there's a sense that Brown's research into Freemasonry failed to yield the kind of blockbuster conspiracy theory that made his name. It's no secret that George Washington was a Mason, and the parallels Brown draws between ancient and modern scientific thought, while enlightening, do little for the momentum of his narrative.

The pace is further slowed by long-winded metaphysical discussions of obscure concepts such as "universal consciousness" – a problem stemming from Brown's fascination with noetics. Founded by a former astronaut following an epiphany in space, California's Institute of Noetic Sciences has made little impact in the arena of peer-reviewed science with its assertions that human thought can transform the physical world. That, writes Brown, is simply because noetics is "science so advanced that it no longer even resemble[s] science".

The movement's dubious principles suffuse the book – Langdon's love interest is a glamorous noeticist who has, we read, conclusively and irrefutably answered the question of whether there is life after death. It's uncomfortably reminiscent of the mass of substandard novels that serve only as promotional vehicles for zany New Age philosophies.

This is more than that, of course. The cryptic traditions of Freemasonry provide for interesting historical insights, and the diabolical schemes of Brown's cartoon villain keep the plot ticking along. He does well, too, to bring in the CIA, even tackling the controversial subject of waterboarding, giving a contemporary relevance to his treatment of secret societies.

Whatever its merits, The Lost Symbol was always bound to sell millions to Brown fans eager for a sensational new dose of religious conspiracy theory. But as it chases one red herring after another, this novel smacks of a hugely successful author getting carried away.

The Lost Symbol By Dan Brown, Transworld £18.99