By Steven Spruill

St. Martin's. 278 pp. $17.95

As subgenres go, the medical thriller is one of the toughest. Its structural requirements are unforgiving; so are its standards of scientific accuracy. The works of Robin Cook are so frequently held up as models that any author who seeks to write a book such as the one under review must inevitably find himself being judged against his mega-best-selling antecedent. Steven Spruill's new novel, "Painkiller," stands up pretty well to such a comparison, and even succeeds in saying something new once in a while. It is a refreshingly unpretentious book, whose central idea is as intriguing as they come; and though its warnings are unequivocal, they are not shrill.

Spruill's first works, such as "The Imperator Plot," were science fiction, and Spruill has learned an important lesson from his apprenticeship in that field. Science fiction readers hate expository lumps. No matter how alien the terrain or how arcane the science, they demand a seamless integration of plot and matrix. As a result, science fiction writers learn early to expound on the fly, to fill their stories with tip-of-the-iceberg details that allow the reader to deduce the contextual landscape. Spruill has learned well: There's no wastage in this novel, and its plot works itself out with the elegance and rigor of an algebraic proof. It is indeed entirely possible that the lack of excess poundage may prevent the book from achieving the sales it deserves.

As frequently with this subgenre, the plot centers on a young female resident of a busy hospital in a major city, and plays heavily on people's paranoia about the medical profession. In this case the city is Washington, the resident is one Dr. Sharon Francis, and the paranoia is made concrete by the fact that at first the only witness to the clandestine hugger-mugger at the hospital is Sharon's mother, a paranoid schizophrenic.

Sharon is no superhero: She's a mass of neuroses herself, scarred by the memory of her father's abandonment of her and her schizophrenic mother. She is drawn toward schizophrenia therapy at the hospital, but her personal life makes her motives suspect. When patients, many of them certifiable, begin disappearing mysteriously after checking out "against medical advice," Sharon is at first unable to prove foul play, and becomes a kind of reluctant gumshoe, stepping on the toes of all her superiors in the process.

There is a well-mixed assortment of characters: obsessive hospital authorities, quirky patients, conflicting love interests, disbelieving policemen -- the tropes of Hollywood are present in abundance, and the book could be converted into a screenplay with only a few minor format changes.

What makes "Painkiller" rise above its cliche-dominated field is the complexity of Spruill's thoughts about his subject. When the evil is finally unmasked, it isn't a matter of the light overcoming the dark but a genuine moral dilemma. Schizophrenia is sympathetically and accurately dealt with, not used as a code word for lunacy. Sharon Francis's feelings about her father are tellingly contrasted with the more idyllic, but equally obsessive, relationship between her antagonist and his child.

Despite its many virtues, however, "Painkiller" is at times laughably predictable. This reviewer had no trouble identifying the real villain or anticipating any of the plot twists. There's an almost paint-by-numbers quality about the way these things are foreshadowed. The scene (an absolute requirement in all novels of this ilk) in which the "mad scientist" Reveals All to his hapless victim is the only expository lump in the novel, and the revelations are, indeed, fascinating. But the climax seems perfunctory, perhaps because many readers will have already figured it out, perhaps because Spruill's prose, here and at other places in the novel, does not rise to the occasion.

Perhaps the most annoying thing of all about this climax is this: We have a heroine -- a strong, complex woman -- who has managed, almost single-handedly, to expose a medical scandal of shattering proportions and to track the villain to his very lair ... yet she spends the moment of climactic revelation strapped to a table, waiting for the handsome hero to come busting in!

I'm sorry that Steven Spruill felt it necessary to enslave himself to the conventions of popcorn fiction, because, potentially at least, this novel is far more than just popcorn. It raises important issues about medical research without resorting to pat answers, and shows a real talent for illuminating character. As the author becomes surer of his medium, he will undoubtedly decide to take greater risks, and the field will be the richer for it.

The reviewer's latest novel, "Moon Dance," has just been nominated for the 1989 American Horror Award.