A leading case, according to Kay, is David Ray Griffin, a former professor at the Claremont School of Theology who has devoted his retirement to writing no fewer than 11 books that examine each minute of the 9/11 timeline. Then there is Paul Zarembka, a professor of economics at the State University of New York, Buffalo, who has scrutinized “such arcane subjects as the price of individual airline stocks in the run-up to 9/11, and the tail numbers of the hijacked 9/11 aircraft.” And Barrie Zwicker, a mainstream Canadian journalist turned truther, insisted on interviewing Kay while Kay was interviewing him, hitting buttons on a chess clock to regulate the amount of time each had.

Once upon a time such people would most likely have operated in relative anonymity. But with the emergence of the Internet, Kay says, they have established their own cult followings, along with the sense of superiority that is created by seeming to enjoy direct access to what actually makes the world tick. Kay writes: “Many true conspiracy theorists I’ve met don’t even bother with Web surfing anymore. . . . From the very instant they first boot up their computer in the morning, their in-boxes comprise an unbroken catalog of outrage stories ideologically tailored to their pre-existing obsessions.” As Kay sees it, the Enlightenment is itself at stake. His verdict could hardly be more categorical: “It is the mark of an intellectually pathologized society that intellectuals and politicians will reject their opponents’ realities.”

But is America really in such dire straits? Hardly. Kay’s description sounds more reminiscent of Weimar Germany or other societies in a state of intellectual collapse than the habitual din and hubbub of American democracy. In concentrating so narrowly on truthers, Kay describes them superbly, but he may exaggerate their potential influence. He asserts but does not demonstrate that 9/11 “has had far-reaching social, political and psychological consequences that have yet to be fully absorbed or understood.”

Then there is the problem of organization. At times, Kay’s book can itself appear almost as convoluted as a conspiracy flowchart. He has a habit of hopscotching between topics and eras. It would also have been helpful had he drawn a clearer distinction between the muckraker, who exposes unpleasant truths, and the conspiracist, who weaves them into a fantastic plot aimed at deceiving the credulous.