Summertime and the Reading Is Easy : Seeking a Serial Killer : Coroner Kay Scarpetta reprises her role as sleuth on the trail of a killer : FROM POTTER’S FIELD. <i> By Patricia Cornwell (Scribner: $24; 412 pp.)</i>

What the world needs now may not be another serial killer novel, but if we’re going to get them anyway--and we are--we could do worse than Patricia Cornwell.

Cornwell is the author of “Postmortem,” “Body of Evidence” and others in the series featuring Virginia Chief Medical Examiner Kay Scarpetta. Cornwell knows whereof she speaks, having worked for six years in that same office, and this is what lifts “From Potter’s Field” several rungs in serial-killer-novel-hell: We learn something. It may not be the function of entertainment to be instructional, but superior fiction almost always is in some way, whether we glimpse some truth of the human heart or learn how we elect our public officials. In Cornwell’s new novel, we learn about forensic medicine, maybe more than we would care to.

On Christmas Eve in Central Park, psychopath Temple Gault murders and mutilates a homeless street girl who has a shaved head and unusual dental work. Her identity is unknown and a key to the plot. Gault is known to the FBI and to Scarpetta. The Feds call her in on the case; Scarpetta’s Christmas is shot. This may explain why she spends much of the novel angry, depressed, having anxiety attacks and arguing with everyone around her.

Gault has disappeared into New York City’s subway infrastructure, has tapped into the FBI’s artificial-intelligence computer network and is now taunting Scarpetta with subtle clues and not-so-subtle murders. The victims pile up. A Richmond sheriff’s deputy referred to as “Sheriff Santa” and two policemen are killed in signature ways. The sociopathic Gault has an obsession with the coroner and seems to be courting her in a bizarre way even as he threatens her.

The plot of “From Potter’s Field” is complex and convincing. As a police procedural, it is fascinating and original. The problems that arise may not bother fans of Cornwell’s, but are worth comment. The characters are malnourished by the author to the point of anemia. With the exception of Scarpetta’s friend Capt. Pete Marino, everyone is completely devoid of humor, no one more so than Scarpetta. Granted, this is not a comedy, and forensic medicine and serial killers are hardly thigh-slapping propositions, but the protagonist’s disgruntled grimness and consistently foul mood are distancing.

The best characters, again with the possible exception of Marino, are dead or remain offstage. The Jane Doe victim implies a fascinating study in a lost soul; the dead sheriff’s deputy promises much in the way of a realistically corrupt cop; Officer Jimmy Davila, dead when we meet him, makes us wish we could have known him better. The major problem is we never really get a good look at Gault, much less a sense of what motivates him, because we spend most of our time with Scarpetta.

In a didactic aside, the medical sleuth describes herself this way: “My disposition was built upon many layers of pain and sadness that had started with my own when I was young. Then over the years, I had added. Every so often I got in moods that were dark, and I was in one now.” This kind of grim self-pity may be realistic, but if you prefer your heroines (and Cornwell does render her heroic) to be sympathetic, this may present an obstacle.

Another distraction along the way is the constant reference to events that a first-time reader would have to assume occurred previously in the series. Scarpetta’s ongoing affair with FBI man Benton Wesley seems to have a history; then there is her relationship with her niece; the death of her husband; the break-in at an Engineering Research Facility that affects events in the current novel; and the case history of Gault himself. Whether or not Cornwell dealt with these elements previously, here they are unrealized background sketches.

“From Potter’s Field” is good entertainment and provides enough chills to keep you shivering at the beach. I just wish I had learned more about Gault--and I wish Kay Scarpetta had been a little more fun to hang out with.

“From Potter’s Field” is also available (abridged) read by Patricia Cornwell on four audiocassettes from Simon & Schuster ($24).