Buying a Mary Higgins Clark book is like buying a ticket to ride the roller coaster. We know we aren't going to the opera, but so what? We signed up for thrills, not trills. Clarks's books are as sure as the roller coaster, too. We strap ourselves in and, once on the track, we're there until the ride is over.

There are no ambiguities in this or any Clark book. We know whom and what to root for, and we do. Similarly, we boo and hiss or gasp when the author wants us to. Clark is a master manipulator.

There are gimmicks galore, often repeats from her earlier books (the lost object which figures in the solution, for instance), but the gimmicks work. There are improbabilities (the coming together of the cast, in this case, which might have been okay in a less urban setting), but we swallow them. And by the time the coincidences seem piled a bit too deep, there's just one audacious hill and one wicked left turn ahead, so we might as well hang in there. We accept the Mary Higgins Clark formula. That's given when we plop our money down.

In "The Cradle Will Fall," as in "Where Are the Children" and "a Stranger Is Watching," we are presented with a threatened heroine, a murderer whom we meet early on, an imperiled domestic stituation, a budding love interest. The mingling of these is standard with Clark, but her readers, and we are legion, expect to find these elements and would be crushed if they did not appear.

In "The Cradle Will Fall" we get a bonus, though. We get a dastardly scientific plot, a la "Coma" or "The Terminal Man."

The heroine in this book, Kate DeMaio, is legitimately lonely. As a judge's widow emerging from her grief, she is guaranteed a sympathetic response. But Kate also fills the bill in other ways: She is young (28), intelligent (an assistant prosecutor) and in immediate danger (she has witnessed the tail end of the dark deed around which the plot, including her own jeopardy, hinges.)

All of this information is given in a brief first chapter, and that's worthy of comment because it is evidence of Mary Higgens Clark's skill. It is upon rereading, for instance, that it seems so clearly expository that the first question rescue workers ask, having loaded the injured Kate into an ambulance is, "How old are you, Mrs. DeMaio?" Tackling this book as it is meant to be tackled -- as an afternoon's entertainment -- the sence reads the way Clark wants it to read.

The murderer appears in chapter two, and here, because he's an obstetrician/gynecologist, we respond with a sure shiver. Clark adds a nice touch of horror here, as we read the man's cold, third-person journal: "At 8:40 p.m. this physician was locking the rear door . . ." It is, really, wonderfully creepy.

We allso side with the person we know will be the prime suspect, the husband of the latest victim. Clark sets us up so that we know, in chapter four, that his relationship with another woman is, as we overhear said woman protesting, "totally innocent." We also discover, not too later on, that the victim was a roaring bitch anyway.

The only other major character is Richard Carroll, Kate's chance for a happily-ever-after. From the start, what we expect is that he solve the case and, in the process, save Kate (at one point, Clark gives Richard a terrific nearsave, the kind that makes you want to break through the pages and tell him what he should be looking at).

All of the minor characters matter, in plot as well as in terms of filling out the world of the book. They are a believable bunch and often they provide the who ? or the huh? or the what-does-she-mean-by-that? that keeps us moving from chapter to chapter, peak to peak, Some, like the mysterious Dr. Jiro Fukhito, add to the suspense, while others, like the loquacious Edna Burns, offer comic relief.

We come out of the book with few complaints -- maybe that the villains's end was all too swift or all too convenient -- but we come out satisfied.

This is good commercial fiction. It is not meant to have resonance, to evoke specific memories once the book is done. It is meant to leave a vague memory, that of having had one great rush of a good time. All of which is to say that "The Cradle Will Fall" is never subtle, but always effective.