uried in the 374 pages of ''Corpsing,'' the British writer Toby Litt's exasperating second novel, is about half of a first-rate psychological thriller. It emerges shortly after the bouts of high-art posturing that mar the novel's first 50 pages and then holds sway -- albeit fitfully -- until the eruptions of wild implausibility that damage its final hundred. That excellent half-book concerns the efforts of a young Londoner named Conrad Redman, a freelance editor of television promos (but he really wants to direct), to reassemble his life after being shot in a fashionable Soho restaurant with his former girlfriend. She -- Lily Irish, an actress best known for her cereal ads on television -- dies instantly from her wounds, but Conrad manages to pull through. Waking from a six-week coma, he gradually recovers from the physical trauma of the shooting and sets out on that old but ever-fascinating quest: to find out who wanted the two of them dead and why.
Before getting to that point, however, readers must survive a trauma of their own -- bombardment in the book's early pages by a salvo of literary special effects. In a now-familiar postmodern ploy, Litt provides us with a collection of interpolated documents loosely related to the narrative, including Conrad's hospital admissions report, a tabloid news clipping about the shooting and even some specious ad copy from the makers of the crime weapon. (''As this catalog goes to press, the .40 ESP has test-fired over 37,000 Smith & Wesson rounds without malfunction: no failures to feed, no stovepipes, no jams whatsoever!'') These are supplemented with italicized sections minutely describing the trajectories and anatomical consequences of all six rounds fired. (''As the bullet passes through the cohesive but elastic tissue of the muscles, a cavity of greater diameter than the bullet's own is temporarily created -- around and behind it.'') Faced with such gratuitous embellishments, one can't help thinking of Elmore Leonard's supremely sensible advice to writers: to ''leave out the part that readers tend to skip.''
Equally unwelcome are Litt's forays into self-conscious showboating: ''Blood. Lots of blood. Blood everywhere. Blood all over. Blood pooling in Lily's lap. Blood in a fine misty spray on the mirror shattered behind her. Blood jumping from her chest wound, like a heavy red frog.'' This particular litany goes on to include almost two dozen similarly hemocentric sentence fragments. We then encounter the line ''Blessedly, I lose consciousness'' -- a sentiment to which many readers, I suspect, will be tempted to cry, ''Amen!''
All of this makes for a discouraging start. But then -- quite suddenly and without discernible explanation -- Litt decides to put most of the gimmickry aside, and ''Corpsing'' instantly improves. In fact, when he allows himself to tell his story without the stylistic high jinks, Litt proves that he can write very well indeed. He is a shrewd satirist, and manages to enliven the familiar investigative process of chasing down leads with some truly clever riffs on everything from comedy clubs to modeling agencies. (My favorite: Litt's withering take on the Royal Shakespeare Company, with its population of ''messianic middle-agers who, whenever a line comes through as if written in modern English, plant it in the audience like a flagpole: this is why Shakespeare is still relevant, why he still speaks to you, why we need more funding.'')
These satirical flights are an enjoyable diversion, and may even be inspired enough to earn Litt that introductory membership in the British Bad Boys Club (Martin Amis, president; Will Self, secretary) to which he apparently aspires. To his credit, however, he never forgets that he's writing a crime novel. Litt takes pains throughout to fulfill the page-turning requirements of the genre, and as his hero begins to unravel the daisy chain of deceptions behind what he thought was a love relationship, the narrative remains propulsive.
Revelations come at regular intervals: that Lily was pregnant when she died, that the father might have been a lover Conrad never even knew about. And while some of the novel's plot devices -- like the pair of tidily contrasting goons (one albino, one black) who start tailing Conrad all over town -- may be a little stale, Litt seems to be aware of this and at times even draws our attention to it. When, for instance, that classic anonymous threat, ''We know where you live,'' is left on his answering machine, Conrad knowingly speculates that it is ''too much of a cliche to have actually come from someone wanting to scare me.''
Meanwhile, Conrad's emotional journey takes on some interesting dimensions in the book's middle pages. Feeling betrayed by his past, he begins to find within himself new reservoirs of anger and assertiveness. He becomes unpredictable, even in his own eyes, increasingly capable of almost any action, so that he must consciously curb his rising sense of resentment toward Lily: ''I didn't want to rewrite my history of her too much -- if I did, it might take away too many of my current reasons for living.'' Conrad's need to discover the truth thus comes into conflict with his desire for self-preservation, adding a potent and dynamic element of psychological danger to his quest.
But then Litt goes too far. Beginning with a scene in which his narrator falls into bed with the most unlikely character imaginable, unpredictability starts to look more like forced outrageousness. In the final chapters, Conrad's transformation from agonized detective to violent avenger seems ever more contrived. And the novel ends with an over-the-top climax that abandons all plausibility in the name of maximum sensationalism.
Ultimately, the problem with ''Corpsing'' may be traceable to an uncertainty of purpose. Litt tries on attitudes the way some people try on shoes, walking a few steps in each, no matter how uncomfortable, before turning to the next. And since he seems unsure about whether he wants to embrace, deconstruct or subtly parody the thriller genre, the book lacks conviction at crucial moments. The result is a curiously frustrating novel. There is evidence in its more successful pages that Toby Litt is capable of writing the smart, thoughtful thriller that we devotees are always hoping for. But ''Corpsing,'' alas, isn't it.
Gary Krist's most recent novel is ''Chaos Theory.''