Black Hornet, if such a term isn't overworked, is crime fiction as postmodernist literary discourse. But before you run a mile to cuddle-up again with dear old Aunt Agatha again, be advised that it is also a cracking good read.

These two books - Shames' fourth novel and Sallis' third Lew Griffin mystery - point up many of the byways down which crime writing can travel. Shames, for example, is following a well-worn path, albeit with no little finesse and good humour. His Tropical Depression is born of Hiaasen, out of Leonard; maybe a dash of James Hall for spice. Sallis' Black Hornet is a different kettle of fish entirely: only ostensibly a crime novel, it delivers the firm smack of ironic distance over and over, baiting the reader to take it seriously. The distinction is in how the two books handle that staple of crime: plot. Shames makes it count as hook for his humour; Sallis barely cares.

Shames' plot is a good one mind. Murray Zemelman - the so-called Bra King - is in a mid-life crisis. He's found much money and a certain satisfaction in lingerie, but now it's all business and a clinging trophy wife. What he really wants is to flee this claustrophobic life, patch-up relations with his first wife, and spend some of his fortune. Thus he packs his Prozac and drives south, meeting Tommy Tarpon, sole survivor of an Indian tribe - the Matalatchee - with half-hearted claims on a small island off of Key West.

Ever the businessman, Murray soon realises Government statutes smile on this unlikely pair - get the island recognised and they can open the area's first legal casino. Throw in Shames' series heavy Charlie Ponte and his in-the-pocket Senator Barney LaRue, and the stage is set for a hearty battle of wits and wills.

Fine stuff then, better even than the most recent efforts (Stormy Weather and Out of Sight, respectively) from either Hiaasen or Leonard. Shames anchors all this with a genuinely smart bit of plotting, paints it with first class screwball humour, then exercises his neatly-drawn and eminently likable characters. His ear for dialogue is as sharp as ever. Slight it may in the end be, but real talent is needed to make it all look as effortless as this.

Effortlessness is something James Sallis is equally versed in, but well-greased plot-mechanics are something else. His book is set in a sweaty New Orleans in the late 60s. Activism is boiling on the streets and a sniper stalking the rooftops, targeting white folks. The press are interested, but black debt collector Lew Griffin isn't especially until - bang! - the sixth victim, a woman journalist, falls right in front of eyes. He is, naturally, a suspect.

Sallis is on record as saying he "could care less for plot. I get very bored...as reader and as writer." A Sallis detective novel, perversely, is about what falls between the cracks of more traditional fare - Black Hornet owes more to the 'literary fiction' conceit of the unreliable narrator than to Shames' rollicking sense of entertainment. Much of Griffin's 'investigation' consists of him sitting at home reading (Camus, Chandler, Himes, The Plague, Don Quixote, Melville and Poe) while the others bring the plot to him.

That, in a sense, is what marks the difference between these two books. Shames is writing crime as amusement, as (outstanding) airport novel, while for Sallis it is a hook, a support for the puzzle we are asked to decode. Time and again the careful reader (and it is easy to ingest this book as simply sloppily plotted genre writing) is brought up sharp by the sense of artifice Sallis is about submerging in his writing. We are unsettled by huge investigative leaps and Griffin's sudden vaults into the future, lifting us out of the narrative to comment on what will happen even after his story ends. Sallis wants to harmonise detective fiction and 'literature' and succeeds so well that, like Walter Mosley, we scarcely even notice.