The thrill is gone in Dick Francis's newest thriller

Bolt, by Dick Francis. London: Michael Joseph Ltd. 240 pp. 9.95. ``Bolt,'' Dick Francis's latest novel (his 25th), has all of the key ingredients for a superlative Francis thriller. Unfortunately, it doesn't thrill.

The hero, Kit Fielding, is the steeplechasing jockey-hero from ``Break In,'' Francis's last novel. Fielding was one of the author's most winning heroes. He was charming, thoughtful, and courageous. Human, too. It is a pleasure to meet him again.

This latest book opens three months after the close of ``Break In.'' The cast of characters is much the same: the Princess Casilia and Roland de Brescou (her husband), Danielle de Brescou (their daughter), and the ancient, forgetful horse-trainer, Wykeham.

In ``Break In,'' Kit defended his sister and her husband - and in the end, himself - from vindictive malefactors. He also met, and fell in love with, Danielle de Brescou.

The threat in this newest novel is to Roland de Brescou, a man too sick and old to defend himself. His young and unscrupulous business partner has formed the money-making notion of manufacturing guns out of 100 percent plastic and selling them to the highest bidder. He means to gain de Brescou's consent to this scheme by intimidating de Brescou's loved ones. The Princess, knowing of Kit's previous success against a similar adversary, enlists Kit's aid, and Kit's intervention unleashes a string of violent attacks.

But despite this promising beginning, the Francis thrill is gone. Certainly, there are moments when the pace picks up and one can't turn the pages fast enough, whole chapters where the thrill is present. Were this any other writer, we would have no complaint. But this is Dick Francis and we expect the moon. The Francis formula

After all, Francis has written a string of successful mystery-thrillers; the last few have been best-sellers in both Britain and the United States.

At the core of his successes are his heroes, who are, with few exceptions, the nicest people. They're the kind of people one wishes one knew - the sort one would like to invite to dinner. The kind one would like as friends. When confronted with evil, they do their best to oppose and defeat it. They fight to the best of their human ability, not as some superhero or Rambo would do, but by employing whatever skills they possess, often by the skin of their teeth. They are honest. Honorable. Good. Not boring, but nice.

But that's not the only reason. Francis's understanding of human nature is another. His antagonists are motivated by real passions: greed, envy, malice, pride, stubborness - those same emotions that have been causing trouble since Cain slew Abel.

His novels often involve the world of steeplechasing - sometimes as the central arena for the action, sometimes peripherally. Since Francis was once a steeplechasing champion, this is not to be wondered at. But what is wonderful is that he uses this seemingly small, highly exclusive world as a microcosm in which one can find the broadest range of human emotions.

His writing style is very direct. There is little distance between narrator and reader. The immmediacy is undeniable: One can hardly put his books down. Where `Bolt' goes wrong

But we read ``Bolt'' because we have come to care about these characters - not because we can't put it down. Perhaps the younger business partner is too like former nemeses. Certainly he is not fleshed out as well. Or perhaps, having read ``Break In,'' we know that Kit Fielding is more than capable of handling such a one.

In all ``Bolt'' seems to be only a post script to ``Break In.'' But like the post script at the bottom of a letter from a friend, it is a pleasure to read and we wouldn't miss it for the world.