BOOK REVIEW / FICTION : THE RATIONALIST <i> by Warwick Collins</i> ; Simon & Schuster; $21, 251 pages : Somewhere Between Logic and Emotion

Dr. Silas Grange, according to his friend and mentor Dr. Hargood, is a “damned wise fool”; Grange has “a mind as cold as winter,” “harbors ‘a terrible detachment,’ ” gives in to no vices whatsoever.

Hargood is a well-known rake, keeping a mistress in London even at his relatively advanced age, but the elder doctor’s voluptuous lifestyle--he’s a libertine at the dinner table, too--hasn’t clouded his ability to judge character.

Grange is indeed diffident, leery not only of appetite but also of simple feeling, and counters Hargood’s friendly charges by pointing out that the madness of Britain’s reigning king, George III, could be attributed to “an excess of emotions.”

Hargood isn’t convinced, and goes on to warn Grange that his faith in reason--itself a contradiction, as Grange at some level acknowledges--may lead to trouble. Hargood even has a source of trouble in mind: Mrs. Celia Quill, a widow in the doctors’ rainy coastal village whom Grange, uncharacteristically, will admit to noticing.

In three short years, Quill has become a respected presence in Lymington, Hampshire, and Hargood admires her greatly, but fears her charm and intelligence will precipitate the ruin of his sensually innocent colleague. “I believe your curiosity will lead you to Hell, sir,” Hargood informs Grange, speaking--so author Warwick Collins tell us--”as though Hell were merely a district, like Cheapside, which a gentleman should attempt to avoid.”

“The Rationalist” is a Gothic novel of sorts, with its portentous tone, bleak locale and early 19th-Century setting. But Collins, for whom this work is not only a U.S. debut but a major fictional departure--his three previous books having been thrillers set in the yacht-racing world--has written with modern sensibilities in mind, for at bottom Quill is a woman seeking equal opportunity.

Naming the field in which she plays the presumptively male role would give the book away: Suffice it to say that Grange does fall prey to her seductive intellect and is later stunned to discover that he has served not some larger philosophical goal, as he had been led to believe, but Quill alone. Or are things even more complicated than that--has Quill, in the final analysis, been honorable all along?

That question lies unanswered at the close of “The Rationalist,” Collins (improbably, also a professional yacht designer, the inventor of the tandem keel used in America’s Cup racing) interested not in rightness or wrongness, but in the vast expanses of the head and heart in which humans routinely delude themselves.

“The Rationalist” is at times quite fascinating, as we watch Grange attempt to incorporate sensuality and tenderness into his world view. He is a man of medicine, after all: In the book’s opening pages, Grange amputates a seaman’s gangrened arm, with rum the only anesthetic, and is well aware that the doctor’s skills rely on the ability to detach oneself from the pains and pleasures of the body.

Grange’s detachment is forced, however, for unlike Hargood--who says, “A doctor cannot afford sympathy. . . . Sympathy is a mechanism for making two people unhappy where only one was unhappy before”--he is introspective, unwilling to let contradictions lie. That’s why he studies David Hume’s “A Treatise of Human Nature”--because Hume, he tells Hargood, is “my Lucifer, my devil,” arguing that reason is no more than dressed-up rationalization and subverting every proposition Grange takes for granted.

It’s interesting that Grange describes Hume in satanic terms, because the ominous, melancholic quality of “The Rationalist” in general, and Quill in particular, lead the reader to expect a bloody, demonic or otherwise darkly romantic conclusion. And in some ways it is bloody: Grange is devastated when Hargood uncovers Quill’s incriminating past, and is bled by his friend, according to contemporary medical practice, “to keep him to his bed.”

Yet the book, which stakes high and original ground, seems attenuated nonetheless, lacking a strong and compelling finale: We’re left feeling ambivalence toward Grange’s relationship with Quill, unable to condone it or condemn it. “The Rationalist” stands tall on its own merits, but one hopes Collins will reread Mary Shelley before his next venture into this genre.