A Hero to His Physician : LORD BYRON’S DOCTOR <i> by Paul West (Doubleday: $19.95; 352 pp.; 0-385-26129-2) </i>

The time was the summer of 1816; the place, the Villa Diodati on the shores of Lake Geneva; the characters and plot so rife with Gothic-Romantic potential as to inspire--as it did, alas--a Ken Russell film.

Here George Gordon, Lord Byron, already renowned and notorious for his poems and his shocking conduct (a true celebrity also in the curiously modern sense of being famous for being famous), fled in the wake of a scandalous separation from his wife. Accompanied by his young physician/traveling companion John William Polidori, Byron met up with Percy Bysshe Shelley, Shelley’s mistress and soon-to-be-wife Mary Wollstonecraft Godwin, and Mary’s stepsister Claire Clairmont. The teen-aged Claire, an early version of the modern groupie, had met--and thrown herself at--Byron in London in the spring of that year. By the summer she was pregnant with his child.

Byron at 28 was the oldest of the company, Claire at 17 the youngest--with the exception of Godwin and Shelley’s son William, known as “Willmouse,” who was less than a year old.

That summer, Byron wrote “The Prisoner of Chillon” and “Darkness,” his powerful vision of apocalypse as entropy which begins “I had a dream, which was not all a dream. The bright sun was extinguished, and the stars / Did wander darkling in the eternal space . . . .” Shelley wrote his pivotal poems, “Hymn to Intellectual Beauty” and “Mont Blanc.” And one dark, presumably scary, night, the group set themselves the task of writing ghost stories, a game that eventually gave birth to Mary Shelley’s astonishing novel, “Frankenstein.”

Then, as now, speculations about the strange menage abounded: Was Claire Shelley’s mistress as well as Byron’s? Had Byron, who was bisexual, found his way into Shelley’s bed? Relatively few speculations, then or now, have focused on Polidori, who remains a kind of footnote to a footnote.

Half Scottish, half Italian, “the youngest man ever to receive a medical degree from Edinburgh University,” Polidori had literary ambitions himself. In taking up the case of “Lord Byron’s Doctor,” the accomplished, amazingly versatile writer Paul West is not out to “prove” that the brilliant, rather unstable, young physician was actually a neglected man of genius, or that he was intellectually or morally superior to the more luminous stars in this circle. This novel is by no means an “Amadeus”-style vindication of a lesser light.

What does appear to interest West about Polidori is precisely his secondariness: his resentment at snubs and slights; the love-hatred he feels for Byron and the displaced hatred he feels toward Shelley for being Byron’s friend and equal; and his nonetheless unshakable conviction that this experience marks the high point of his life: “I, however, had fixed on Diodati, the style of life and love there. The longer I was there, the less I was able to think of living in any other way, wolfing the sandwich in which humiliation sat between layers of splendor.”

West, who wrote a nonfiction book called “Byron and the Spoiler’s Art” (1960) and who has explored the bizarre, the offbeat, the grotesque, and the liminal in numerous works of fiction, has an affinity for the least appetizing aspects of Byronism, and in Polidori he has found an eminently suitable mouthpiece for this novel’s potent blend of fact and imaginative hypothesis.

Frustrated, obsessed, unreliable, and more than a little mad to begin with, Polidori is also an anatomist driven by the dissector’s need to see things at their worst, which he calls “deinosis.” He details Byron’s sadistic sexual exploits, his heartless treatment of Claire, his arrogance and self-loathing, in the mode of the scientific medical observer intrigued by strange symptoms, yet in the voice of a young man horrified and fascinated by a slightly older, vastly more glamorous one. The Polidori West gives us embodies that strain of Romanticism which sought to apply the fearless methods of Enlightenment rationalism to the irrational, forbidden, and mysterious realms summoned up in Gothicism. His susceptibility to the power of Byron’s personality manifests Romanticism of a different sort. Here, he recalls their parting in the Alps:

“We embraced once, twice, and I smelled the macassar oil in his hair, telling myself that all the fragrance of the wide world was going away from me now, all the joie-de-vivre and all the celebratedness; I was to pop back into the hole I had sprung from, but irremediably changed. Would I, at this watershed, this sheer drop, get the kiss he reserved for me alone? I did. I kissed him back, and we stayed there hugging in the recoil from the kiss, our cheeks in touch, our lips, our pairs of them, isolated in the spring air.”

West’s feel for the Zeitgeist is matched by his uncanny, ventriloquistic ability to simulate the voices of these historical characters without seeming anachronistic.

By the end of his narrative, Polidori is dead, a suicide at 26, unable to bear the letdown of being dropped from the charmed circle. Yet before then, he tells us what happened to the other characters--this, although he dies in 1821, before Shelley or Byron, let alone Godwin or Claire. (West performs a similar narrative feat in his novel “The Very Rich Hours of Count von Stauffenberg.”) The fiction writer’s attempt to rejoin the magic circle of the past is bound to end in failure. West, like Polidori, is an imposer and something of an impostor. The strength of this novel is that for a little while we accept its imaginative imposition.