The Psychopath Test, By Jon Ronson

Reader, fasten your seat belt. Jon Ronson's "journey through the madness industry" is a roller coaster ride, a rollicking journey which will have you whooping with amazement, gagging with nausea and swooning in disbelief. It is peopled with extraordinary figures, the "diamonds of craziness", and the novelistic style makes it hard to distinguish fiction from reality. It is always entertaining, often surprising and constantly switching direction.

But I kept wondering where it was leading, right to the last page. What conclusion was Ronson going to reach from his international meanderings as a psychopath spotter? I never did find out because there isn't one. The stories are left to stand on their own. Gripping though they are, that was disappointing.

The book begins with the tale of an academic who sent a 40-page text to colleagues around the world with a cryptic message sayingL: "Will tell you more when I return." It created a stir amongst the recipients and Ronson tracks the down the author - a distinguished psychiatrist and protein chemist. He is dubbed a "crackpot" by one who knew him, and that would have been good enough for me. But it sets Ronson off on his quest - to discover if society is quite as rational as it seems.

Next he is introduced to Tony, a resident of Broadmoor, who claims he is well and has been admitted by mistake. He said he faked his way in and now can't persuade the psychiatrists to let him out. It is the Scientologists who introduce Ronson to Tony, which maybe should have provided a clue.

Then he goes on a course in psychopath spotting, based on a 20-point checklist with items like "grandiose sense of self-worth", "shallow affect" and "parasitic lifestyle" - with which it is apparently possible to identify mental disorder. Ronson naturally sees it everywhere, especially in political leaders and businessmen.

One of these is Al Dunlap, an American who made his fortune by buying up companies and cutting them down to size, without apparently shedding a tear for the thousands laid off, their lives and dreams destroyed. Until he got sacked himself, when his son chortled with glee.

Ronson interviews a television journalist who hires people for reality shows according to what pills they are taking. They have to be not too mad, but "just mad enough", having the kind of madness with which the audience can identify. So depression, signalled by Prozac, is in but schizophrenia (anything stronger) is out. How weird is that?

I think I am beginning to get the message now. The world is full of weird people. He interviews David Shayler, ex-MI5 agent and conspiracy theorist who claimed the 7/7 bombings never happened - the explosions were caused by a power surge and the government had to cover it up. Later Shayler claimed the 9/11 planes were holograms. On both occasions he got extensive press coverage. But when he said he was the Messiah, he was ignored. That was too mad, even for the wilder shores of the tabloid press.

The most gripping section is his account of the Colin Stagg case. Stagg was the man wrongly accused of the Wimbledon Common murder of Rachel Nickell, after the police set a honey-trap for him based on psychological profiling provided by Paul Britton. It is said that Britton provided the model for the Robbie Coltrane character in Cracker. Unfortunately, the real-life Britton couldn't match the fictional Cracker. Stagg eventually won £706,000 compensation. A test for psychopaths? I don't think so.

Jeremy Laurance is health editor of 'The Independent' and author of 'Pure Madness' (Routledge)