The Lost Symbol. Dan Brown. Doubleday. 509 pages. $29.95.

Dan Brown takes on some whopping metaphysics in his new book: ``What happens to the human condition if the great mysteries of life are finally revealed?'' Good question. Pity he doesn't bother to answer it. Perhaps there are no definitive answers, but when a book alludes to someone's ability to solve, say, the mystery of what happens after we die, a reader expects to learn what that process entails, not to wade through a lot of historical mumbo jumbo about symbols and allegory and how the Freemasons are really good guys. That's not what we're here for.

The Lost Symbol is full of such empty teases. Maybe the idea is to provoke us to allow our imaginations to roam unhindered by logic. Fair enough. But the book is supposed to be a thriller, and it reads more like a primer. Call it Freemasonry 101. There are a few chases and several ugly acts of violence, but most of the characters prefer to talk rather than act, which would be fine if only their conversations weren't quite so repetitive and simplistic and if much of the talking wasn't just a device for the author to set up his deepest perplexities.

This time The Da Vinci Code's symbologist Robert Langdon is called to fill in as last-minute speaker at an event hosted by his friend Peter Solomon, head of the Smithsonian Institution. At least, that's why Langdon thinks he's leaving the relative safety of Harvard in such a rush. Turns out he has not been lured to Washington, D.C., by Peter but by a madman who calls himself Mal'akh. This sadistic, tattooed eunuch -- of course he is a eunuch! -- is holding Peter hostage and will only free him if Langdon helps him solve a tricky, potentially dangerous Masonic riddle. Mal'akh, we learn, is a former drug runner who logged time in a Turkish prison and is fond of speaking like a 1940s villain (``That which your brother believes is hidden in D.C. . . . it can be found''). He also enjoys blood sacrifice.

As the race for answers grows more deadly, and Langdon runs all over the nation's capital, others become involved, notably a tough-talking CIA operative with murky motives and Peter's sister Katherine, a scientist working to solve philosophical mysteries through physics.

Brown reuses many of the devices that made The Da Vinci Code so popular: Famous landmarks (the U.S. Capitol, the Washington Monument) play a large role, and he delves into the inner workings of a secret society (Opus Dei in Da Vinci, Freemasons here). Stylistically, nothing much has changed. Brown writes short chapters that end on breathless cliffhangers (``Something was very, very wrong''; ``My God . . . I've made a terrible, terrible mistake''; ``What happened next, Langdon never saw coming''). He can never be accused of being an elegant stylist, and his fondness for cliché is legendary. Cellphones ``cut the night air.'' Bad guys are ``salivating like a lion about to consume his injured prey,'' and more than one victim is unnerved by ``inky blackness.''

But such lapses can be forgiven if you've got a compelling story. The Da Vinci Code, for all the backlash it inspired, dared to tamper with the tenets of Christianity and to offer up an intriguing conspiracy; its payoff was strong, and that's what we remember. The Lost Symbol feels more like a lecture that's occasionally interesting but still a lecture, and its payoff is virtually nonexistent. Worse, Brown tries to pull off a cheap trick late in the book that's supremely nonsensical. You'll know it when you see it.

Of course criticism won't matter. The Lost Symbol is destined to sell well, and plenty of fans will enjoy it, especially if they've never read much about the Masons, our founding fathers or any of the great philosophers. The book will definitely increase tourist attention to the ceiling above the Capitol Rotunda. But Brown offers a warning that feels all too pertinent to this book: ``Wide acceptance of an idea is not proof of its validity.''

Connie Ogle is The Miami Herald's book editor.