The Leather Set : FALL.<i> By Kai Maristed (Random House: $23, 275 pp.)</i>

To experience the electric charge of moving in sync with a tremendous source of power, one that is graceful, spirited, alive--this is why riding horses fills us with joy.

There is little of this joy in Kai Maristed’s elegant though not always seductive novel, “Fall.” This is a hard, cold, gray look at the high-pressure world of show jumping. It is about teenagers who ride not for the pleasure but out of the fear of losing--either ribbons or parents’ affection. It is a toughly told love story that, perhaps not coincidentally, is also about a sport involving leather, boots, spurs, whips, and verbal and physical abuse. A kinky tale of S&M;? That’s how this author seems to see it. Maristed’s take on the exclusive, agonizing and at times murderous world of competitive riding is uniformly dark.

In the fall (the title takes on several symbolic meanings), as days grow darker, damper and colder, young equestrians and their ambitious trainers compete for ribbons and recognition on a circuit of horse shows sprinkled around the New England countryside.

The horses the adolescent riders, and the sometimes cruel trainers and neurotic parents are primarily viewed through the clear eyes of 40-year-old Lex Healey. He’s an outsider in the small exclusive horse world. Lex comes from a working-class Italian-Irish family in Boston. Fed-up taxpayers eliminated his rewarding work with urban kids in an after-school sports program, so he’s accepted a job with an equine security agency, Horseguard International, even though he’s never even ridden a horse. He wouldn’t know the withers from the pastern of a horse but, hey, it’s a job.

The work has also led him to Erica Hablicht, one of the trainers on the circuit, a 35-year-old married woman he has fallen passionately in love with. And she with him.

Their affair plays itself out in tacky, charmless motel rooms as they move from show to show. No matter how discreet they’ve been, everybody (except Roland, Erica’s husband, who is home minding the horse farm) knows they’re an item. And nobody seems to care, except young wheelchair-user Ruthie Pryor.

A former star rider who has been injured in a hit-and-run car accident, Ruthie has been traveling solo from show to show, hungrily eyeing the new kids on the block. Her mind has become as twisted as her legs. “I had a lot of friends once,” she thinks in her agonizing loneliness. The affair between Lex and Erica, which she has observed firsthand, has only increased her psychic torment, driving her to an attempted act of blackmail.

But trouble of a much more sinister nature haunts the show circuit. Valuable champion horses have been dying mysteriously. People have been buzzing about Tom Burns (a real-life figure; see Dick Roraback’s accompanying review of “Hot Blood”), also known in horse circles as “the Sandman.” Clients would pay the Sandman from $5,000 to $25,000 to kill their horses so that they could collect insurance money. Horses have been killed in horrible ways--electrocuted and bludgeoned.

Maristed writes with clarity and terseness, a muscular language: “She wore that naked, horse-starved look.” She gives us spare and powerful descriptions that punctuate the quietly unfolding plot like arias: “Against the blackness, [Erica] saw the aged field hunter, lying with his hooves tucked under his chest. She still held the useless hypodermic. White hairs sprinkled his muzzle, and the flesh of his face was sunken and molded to the bone the way it is with very old ones, giving them a wise experienced look, and he looked up at her steadily, as he died.”

Maristed knows how to bring on a smile. Here’s Erica schooling a student: “Now listen good. He’s tired. Gas him in the opening circle. Wake him up. The first line’s long--ride like you mean it--but take back before the diagonal line. Watch the triple, it’s a tight three-stride to a two--but give his face room. Got it?” Got it? “Now go have fun.”

Maristed’s horse murder plot comes to a rather hackneyed conclusion. She resolves the love story, however, between Lex and the high-strung Erica in a way that is subtle, sweet, mysterious and feels right.

Meanwhile, Lex has been promoted by the owner of Horseguard to an office position. After a “week of pencil pushing,” he is seized by “a sudden overwhelming urge to be among horses again, to hear and smell and maybe touch a few of them.” He drives out to a sales barn one wintry afternoon. After all, he had never even held reins, he muses.

The cool prose explodes into poetry as Maristed describes what happens to Lex as he lets himself mount a tall, stumbling, clumsy horse named Lancelot. It’s a moment too splendid to miss.