Break In: by Dick Francis (Putnam: $17.95; 317 pp.)

American racegoers admire British racing for its royal descent. When the queen’s best colt at Ascot each summer, in the Epsom Derby preferably, the sport of kings again resounds with the nobility for which it has been named.

Blueblooded horses, noblemen in vested suits, lords and ladies posturing in private boxes, long-distance racing over turf--the splendid traditions continue. And improving the breed, racing’s rationale, still counts most, as it no longer does in the States.

The aroma of race-track mischief in a purple British setting forms a convenient backdrop for weavers of mysteries. Dick Francis has now written 25 of the most popular race-track thrillers ever, selling 20 million copies to a still-faithful following.

An ex-steeplechase rider of England, Francis constructs plots and characters that reverberate as counterpoints to the familiar race-track stereotypes. Francis knows that highbrows might also be crooks. He knows that trainers and jockeys might be intelligent.

Francis understands as well the business of the racing industry and the foibles of most horse owners. All of this correctness accounts considerably for his continuity, along with the crisp, spare prose of his narrative and an ear for dialogue that moves a complicated story quickly toward its climax.

The 25th mystery, “Break In,” represents a leap forward for Francis, his most complex, fascinating story, to be sure, but an unusual character study besides. The effort had possibilities of achieving new heights, except in the end the author fails his main character despairingly. Francis’ books have been testaments to storytelling, firm on plot, setting, and intrigue, slight on character development and interpersonal relations. “Break In” is both a continuation and a departure.

In this tale of scandal, family dishonor, and the power of an unethical press, Francis creates as his protagonist the archetypical intelligent jockey. The character becomes the story. He is Kit Fielding, leading jump-horse rider on England’s major circuit.

The construction of Fielding as super-sleuth works refreshingly for racing buffs, precisely because no one believes for a moment that a jockey might be highly intelligent, not to mention honorable and noble besides. A jockey is a little guy who grew up on a farm who comprehends little of life beyond horses.

As Kit readies to ride in the feature at Cheltenham, his twin sister Holly arrives with desperate news. Her husband, Bobby Allardeck, a minor trainer of thoroughbreds, has been libeled in the Daily Flag. The Intimate Details column claims Bobby has bought yearlings he cannot pay for, is on the skids financially, and his tycoon father Maynard isn’t rushing to the rescue.

None of it is true, but backstretch suppliers demand to be paid, jittery owners begin to pull their horses from Bobby’s stable, and the bank is poised to call the yearling loan. The stable will be ruined; so will Holly and Bobby. They can’t pay the bills.

The Fieldings and Allardecks have been feuding families for generations. The belligerence extends through decades of breeding, training, and racing thoroughbreds. Now his sister calls upon Kit to stop feuding and expose the fraud.

The early crisscrossing trails lead to publishing magnates, owners’ boxes at Ascot, the seamiest streets of London, and back full circle to Kit’s family history. When Fielding collects detailed evidence of wiretapping, a gang of hired assailants begins to chase him, mugging and knifing the jockey at one point.

Francis’ subplots invoke the race-track settings where the jockey as celebrity is riding several times weekly the crack horses of an authentic princess and enigmatic trainer. From Cheltenham to Newmarket to Exeter to Sandown to Towcester to Devon to Ascot, in the manner of the two-day and three-day meetings of England, Fielding continues to accept all mounts and rides on.

The jockey wins repeatedly. While fighting crime and running for his life, Fielding never falters on the course.

But in his sorting out the mysteries in the mannered technique of the expert storyteller, Francis deserts his protagonist. He suddenly turns marvelous Kit Fielding into an extortionist; a con artist for whom the end justifies the means.

Earlier Kit failed to report an attempted bribe to the racing commission, but the oversight worked well as an agreeable chink in the jockey’s otherwise impregnable ethical armor. The deal Fielding concocts in the end, however, sets a high-society robber baron free to rob again, slaps a kettle of violent criminals on the wrist, and--worst of all--sets himself up for bribes and capers later on, probably involving race outcomes.

If the jockey loved racing as much as Francis insists, he must have known that in the unmasking he is not only acting out of character but outside the interests of the sport as well.

It’s a pat ending for the story, but a tragic ending for racing.