By Simon Mawer

Little, Brown. 320 pp. $24.95

Simon Mawer's third novel, The Fall, begins with a fatal tumble on a Welsh mountainside. A chilly voice narrates the last climb and awful descent of world-famed mountain climber Jamie Matthewson, hints at its untold mysteries and the possibility of self-immolation, and then quietly drops a curtain: "He died as they stood and watched."

The Fall's stark opening hardly prepares the reader for the gaping valleys and dizzying peaks of Mawer's latest work. The book's plot simmers with abandoned youthful friendship and slightly sordid love affairs, employing mountaineering and memory as its controlling metaphors, yet Mawer seeks to complicate matters further by slicing up linear time and shuffling narrative voice. Somewhat less intentionally, The Fall also divides and juggles the reader's sympathies. The novel's lurches into botched sensuality and gratuitous twists leave the reader pitying Mawer's unsteady grip on human nature -- and lay bare a hollowness at the heart of his novel. Yet Mawer's ability to thread narrative through his various conceits can also prove exhilirating.

Much of The Fall is told in the present, through a gauze of memory, by Rob Dewar, Jamie Matthewson's friend and climbing partner. A more distant third-person voice relates the course of a sepia-tinged love affair acted out 60 years before. Under the shadow of the Welsh hills and the impending Blitz, another clambering Matthewson (the equally legendary Guy) ensnares the mothers of both Rob Dewar and Jamie Matthewson in a triangle of passion and jealousy. It's a messy tale of naivete and sexual opportunism that takes the crash of Hitler's bombs as its soundtrack, while relying on the privations and prudery of wartime Britain to heighten its pathos.

This wartime tangle of secrets grows still more dense as Rob and Jamie move through childhood, adolescence and young adulthood. The two boys meet by chance and become fast friends, propelled by an achy twinge of laddish homoeroticism and yet more sexual triangulation (including one coupling that's an uncomfortable half-step from the Oedipal). Another tragic fall and dramatic betrayal in Switzerland -- on the Eiger's deadly North Face -- seals those secrets and the friendship under an icy emotional drift until Jamie's untimely death opens them once again to Rob and to the reader.

Mawer's earlier novels, such as Mendel's Dwarf and The Gospel of Judas, smoothly harnessed ambitious ideas to whip-smart narratives. But the knotted contrivances of love and disloyalty at the center of The Fall tend more to simple complication (and even gratuitous shock effect) than to complexity. The novel's ghosts clank drearily and predictably, even in a "Swinging London" that, in Mawer's hands, can't find its hip-swivel. When they are not climbing, the novel's characters are as flat as mountain peaks are high -- all bad jokes, mawkish attempts at high seriousness and stammering stuttering pillow talk. (The Fall's women, in particular, oscillate between the poles of sexual predation and sappiness.)

Yet the novel's various kinks and snags -- its lies, betrayals, flawed characters and mild perversions -- do fall away when the author plays to his strengths. When Rob, Jamie and their mothers and lovers start to climb, Mawer uses the occasion to craft mini-essays on mountaineering and paints gorgeous landscapes. At those moments, the novel ripples with energy and verve.

For instance, Mawer guides readers expertly into the jargon and slang of the mountaineering set with the surest of hands, crafting a solid and physical prose that pulls even the rankest of amateurs upward with it. At one moment, he describes a novice's impression on her third day of climbing, and captures perfectly the blend of growing confidence and continued apprehension: "Every feature in the crags seemed to have a name -- the Captain, the Veranda, the Chasm. There was facetious tone to them, the spirit of enforced jollity and deliberate understatement, the spirit of the past. She panicked when she had to traverse back to the original line of the route. She was expected to cross a smooth slab of rock using sharp handholds alone, her feet just scraping on the holdless rock below, and halfway across her strength gave out. It seemed a sudden thing, like water fluid draining from a tank."

Mawer is even better with the landscapes against which The Fall unfolds. The glum features of a Welsh mining town sigh into flower in his prose ("Slate was the whole world, slate the landscape, slate the sky, slate the rows of terraced houses, slate the road."). When Mawer essays the glories of conquered peaks and the supplicant landscapes below them, his words even evoke comparison with those capital-R Romantics: "At the top, at the foot of the Rote Fluh, the Red Wall, we paused again to look. Below us the ground fell away to distant meadows where there was sunshine and warmth, and a vast slanting wedge of shadow -- a half-mile of darkness cast down the hillside by the mountain itself. The incongruous sound of cow bells drifted up in the afternoon air."

Yes, we've heard this language before, but Mawer freshens it beyond immediate recognition into an active presence. His strengths in guiding us through the nooks and crannies of mountaineering and its stark landscape suggest that he could successfully cast off brain for brawn in his future work. But his lack of skill as a portraitist leads The Fall downward into an emotional chasm from which it never truly ascends. *

Richard Byrne is a freelance writer based in Washington, D.C.