Over the Edge by Jonathan Kellerman (Atheneum: $17.95; 374 pp.)

Jonathan Kellerman’s award-winning first novel, “When the Bough Breaks,” was about child molestation and family secrets. His second, “Blood Test,” was about child abduction and family secrets. “Over the Edge,” his third and latest, is about child persecution and family secrets. A pattern seems to be emerging here, and, surprisingly enough, it is a good one for readers.

The tough detectives of Dashiell Hammett and Raymond Chandler had little time for the underaged, but in the ‘50s and ‘60s, Ross Macdonald’s Lew Archer was frequently moved to action by troubled young people. And in the last few years, three hard-boiled novelists--Kellerman, Andrew Vachss (“Flood,” “Strega”) and Benjamin M. Schultz (“All the Old Bargains”)--have limited their protagonists’ activities solely to cases involving abused children.

The mystery field comes complete with its own rigid boundaries but, oddly enough, the work of these authors seems to benefit from their self-imposed parameters. Kellerman, in particular, gets better with each book, refining his style, replacing melodrama with credible situations, discovering new ways to say more with less.

In “Edge,” his narrator-hero, a semi-retired psychologist named Alex Delaware, is awakened at night by a former patient, young James Cadmus, begging incoherently for help. Delaware has been harboring a bit of guilt over his failure to aid the boy in the past, and so he begins to make his own amends by investigating the circumstances that could have transformed a “difficult” boy with an unusually high IQ into a teen-age multiple-murderer whom the media has labeled, in its quaint way, “The Lavender Slasher.”

Abetted once again by his pal, police Sgt. Milo Sturgis, Delaware embarks on a considerably longer journey toward truth than in his first two books, more than 100 pages longer, but Kellerman isn’t wasting his or our time. We visit a number of Los Angeles’ high and low spots, from mansions in Hancock Park to rat-infested Downtown lofts. There’s a particularly harrowing tour of the maximum security wing of the Los Angeles Police Department and an intriguing side trip out of town to a canyon that may not be as unspoiled as it looks. And, as in any mystery worth the name, clues begin to pay off, evidence piles up and a diabolical evil is exposed.

Kellerman, a psychologist who is presently clinical associate professor of pediatrics at USC’s Medical School, is obviously on firm ground when discussing the workings of the mind. But his expertise doesn’t appear to stop there. I have no idea how much of the material he feeds us is based on research or how much he has made up whole cloth. It all seems totally convincing and involving. The pros and cons of the diminished capacity courtroom plea, the attitudinal differences between Beverly Hills investigators and downtown sheriff’s deputies, what ingredients go into new-wave catered cuisine, the way genius teens converse, the inner sanctums of the UCLA Medical Library--just part of Delaware’s very believable daily rounds.

“Edge” is more than a solid, gripping, page-turning mystery. It is the work of a novelist of uncommon insight and storytelling skill--a novelist powerful enough to survive three of the most unappealing hardcover dust jackets this reviewer has ever seen.