Book: The Street Lawyer by John Grisham (Century, pounds 16.99)

The US is the world's richest Third World nation. Imperial America's decay has one simple cause: the unsustainable tension between extreme greed and extreme poverty. While intellectuals wring their hands, it takes a thriller-writer to mention this unmentionable fact.

John Grisham's new novel opens with the narrator and several colleagues being held at gunpoint. Michael is a rising star in a giant DC law firm; his captor is a down-and-out, who demands to know how much each of his hostages donated to charity during the last fiscal year. Specifically, money to buy "Food for hungry people right here in this city."

Michael responds to this adventure by more-or-less deliberately "cracking up". He resigns his job, and - frightened and excited at the prospect of visiting another planet, 20 minutes' drive from his office, where the poor and black live - he becomes an advocate for the homeless in a country where homelessness is in effect illegal.

Grisham is among the most dialectical of contemporary writers, popular or literary, but The Street Lawyer is a plainly didactic book. It is a curious novel, fluent and fascinating, but not suspenseful and with a strangely fairy-tale ending. This may surprise those who know his work only by reputation. What makes Grisham stand out among authors of blockbusters is his evident determination never to write the same book twice, though he incorporates elements of each in all its successors.

His second novel (The Firm, 1991) made him a multi-millionaire, and gave him the freedom to ignore the rules of publishing. While this has resulted in one or two mistakes ("daft" would be a charitable description of The Client), his work can be seen as a cumulative dissection of the legal system of a kind probably not attempted since Dickens.

With lawyerly precision, in each book he strips away another layer of fashionable marginalia and moral obfuscation from subjects such as racism, capital punishment and corruption. Now, with The Street Lawyer, he has arrived at the heart of the case for the prosecution: hunger in the Land of the Fat.

Grisham's previous book, The Partner, was a satirical fable of a kind rarely sold at airport bookstalls, and this new novel contains some fine, grim comedy. I half-suspect that Grisham is not a particularly humorous man himself, but a skilled writer who has mastered comic techniques through diligent study. He seems to be getting angrier about the betrayal of America, and increasingly favours the neat gag over the dazzling cliff-hanger.

Ironically, it is just because he is the world's best-selling author that he is able to work almost under cover, invisible to mainstream critics. He uses this independence to think for himself - the faculty his readers have surrendered in exchange for their status as middle-class Americans.

No off-the-peg liberal, Grisham's ultimate destination is unguessable. Whatever he writes next, don't underestimate this man. Few writers have so much to say, the skills to make reading what they say an irresistible pleasure - and the clout to be able to say it, when and how they like, to an audience of millions.