WHEN IT'S 92 in the shade it's a dangerous time. Hot, sweltering, no relief until nightfall. Most of life's social niceties and buffer zones have boiled off and what is left is raw will. Thomas McGuane's latest book contains two raw wills, lying as crisp and on edge as dry leaves, ready to burst into flames the moment pressure is magnified. But these particular wills belong to two people who thoroughly know their principles and their capacity for deliberate action. When the collision comes they summon up with heroic energy the grace to die well. It is that which Hemingway demanded of all his heroes, and McGuane depicts it powerfully.

Before these two adversaries--master fishing guide Nichol Dance and encroaching novice Tom Skelton--die their beautiful deaths, McGuane unfolds the recesses of Tom Skelton's psyche. Skelton is a modern Thoreau. A refugee from prolonged drug miasmas and the turbulence of modern society, Skelton has retreated to his hometown to slow down his pace of life and get back to the core of his being, allowing just the essential eccentricities. His Walden is the ocean surrounding Key West.

McGuane is rhapsodic in his meticulous, almost poetic description of the inspiration the ocean offers Skelton--seascapes of rocky bottom and tide-waved weeds; schools of fish gliding instinctively past each other without colliding; the expert crafting from scratch of Tom's skiff; the art of guiding that provides a framework within which Skelton makes his last ditch attempt to integrate his psyche with the natural world. Guiding is a one-man job, but Hemingway style requires full exertion of Skelton's intellect, intuition and physical strength in mastering fishing equipment and tides, navigating channels and neighboring keys, and sniffing out the big permit runs.

UNLIKE MANY characters in modern novels who are paralyzed by a world that looms absurd and meaningless, Skelton maintains deliberate control by asserting the inviolability of his soul. This opens a great margin of humor in the book, for many experiences that would smash a weaker ego simply glance off Skelton. He is intellectually happy-go-lucky. Reflecting McGuane's authorial faith in the power of words to synthesize coherence from a barrage of external events, Skelton continually articulates his perceptions.

Value is found not in objects or personalities themselves, but in the degree they trigger his mind to acknowledge their identity. When Skelton's skiff is finished and he and his girl Miranda haul it to the harbor, he scorns unearned satisfaction:

"It's beautiful," said Miranda. She drove, Skelton constantly looking back to see how it was trailing; the bow loomed in the rear window. "Does it mean a lot to you?"

"It will."

"When?"

"When I have paid for it and put some fish in the box and some hours on the engine. Right now it's just beautiful and beautiful isn't very interesting."

McGuane's prose is precisely crafted and exact, reflecting the high degree of articulation Skelton demands of himself. But it is also extremely fluid, lyrically delineating Skelton's consciousness.

MCGUANE HAS little compassion for those who don't articulate their thoughts and so drift helplessly in emotional weakness. His lack of respect is reflected in the degree to which these characters remain caricature. But antecedents of Skelton's philosophical calculations are seen in his grandfather Goldsboro, head of the Key West mob and financier of the skiff:

If there was a single thing for which he had a gift, besides that of pulling rugs out from under his opponent, it was for a kind of manipulation of conditions so that the problem or the solution seemed fresh to the point of being raw. He had, for example, carefully kept his grandson dancing on a string of unease over this guide boat. On the one hand, he wanted it to be as vivid as only uncertainty could make it; and, on the other, he could not resist the dicey gaming around, the spirals of manipulation that were the actual texture of his life.

McGuane carries the process of Tom's self-definition to its ultimate conclusion as Tom persists in his ambition and courts inevitable mortal opposition from old-timer Nichol Dance over his share in Key West's tourist guiding trade.

Skelton's sense of integrity in acting deliberately becomes an obsession and death no longer remains an abstraction. Tom doesn't struggle to find ultimate meaning in death itself, but in one of McGuane's clever twists, maintains his philosophy and evaluates it in terms of his own identity. Thus, he can speak of death in curiously warm and lighthearted tones because it arouses a gentle fondness for the sensual world he will relinquish.

One applauds these deep resources of spirit which McGuane feels are desperately lacking in the rest of 1973 America. But this approval fades in full view of the tragedy.

The principle which enables Skelton to come to peace with himself is a spark between the metaphysical and physical, so all-consuming, that it destroys any possibility of cooperation.