Something Is Rotten in Rivertown : DOWN BY THE RIVER <i> By Monte Schulz (Viking: $19.95; 432 pp.)</i>

Rivertown, California--an out-of-the-way and deceptively placid-seeming Central Valley community--is the setting for this ambitious debut novel by Santa Barbara author Monte Schulz.

Possessing all the small-town qualities that urbanites often wax wistful over, Rivertown takes some special finding. It’s not included on most service-station maps. Travelers don’t normally choose it as a destination. “You got lost and wound up in Rivertown,” muses its chief of police. “Or else you lived there. It was not exactly the Twilight Zone but sometimes it seemed as though the two shared a common border.”

And before many pages have passed in Schulz’s eventful thriller, it becomes apparent that something is very rotten in Rivertown.

It all begins one sweltering summer night, near hobo jungle in the abandoned railroad yard. A teen-ager named Sarah Miller says she was raped there by a gang of tramps. Armed townspeople form a vigilante group that fires upon the hobos, killing one and wounding 13. But, once order has been restored, none of the tramps can be linked to the sexual assault. And a few days later, after the hobos have left town, the nude and battered corpse of Sarah Miller is discovered floating in the river.

More fatalities quickly follow. Two of Sarah’s male cronies die in a suspicious highway accident. Two more disappear and eventually are found brutally slain. Has one of the tramps returned to wreak awful vengeance on Rivertown’s vigilantes, or is some even more horrible scenario being enacted?

Trying to make sense of it all is Police Chief Carrol Howser, a relative newcomer to Rivertown. A former San Jose police officer, Howser has some personal problems to wrestle with. He’s bothered by the memory of an old line-of-duty shoot-out that he barely survived, and he still misses the wife, who left him on the eve of his move to Rivertown.

Hampering Howser in his work is an obstreperous local establishment led by Tom Danielson. Old Tom, Chief Howser notes, is typical of the sort of privileged folk who “delegate jobs while retaining authority. That way when the screw-ups occur, they can blame the hired help.”

Howser is a well drawn figure. There are several other dimensional characters in “Down by the River.” Jane Crockett, police dispatcher and sometime sweetheart to Howser, is a welcome presence, and a gaggle of vulgar, unappealing teens--led by the sneering Jamie Danielson, Old Tom’s boy--is sketched in a convincing manner.

In addition to creating believable people, writer Schulz (son of cartoonist Charles Schulz) conveys well the texture and tempo of life in his fictional California town. His descriptions are clean and vivid, and his suspense scenes have the right amount of tension. Monte Schulz writes well; no doubt about that.

The problem comes with the plot. People die in this book with alarming--and predictable--frequency. By the time the sixth victim meets his death, a sense of absurdity has set in. Meanwhile, Chief Howser is made to act--or rather, not act--in a most unlikely fashion. Caught in the midst of a bizarre and grisly series of events, the seemingly unperturbed policeman retreats into routine and paperwork, waiting for some ephemeral lead. (“He was not sure what he was looking for yet; he just assumed he would know when he found it.”)

All the while, Howser ignores the possibilities before him. The louts led by the town boss’s son, for instance, are obvious suspects. They have falsely identified as Sarah Miller’s assailants men who were later exonerated, and the petty pranks for which they are regularly arrested are not that different from some more spectacular acts of vandalism that seem connected to the killings. But Howser does not pursue this avenue.

When yet another young person is reported missing, Howser acts annoyed rather than alarmed. He is glad, he says, that all these happenings have not drawn the attention of the big-city press (an unusual non-occurence in itself); and he does little to augment the inadequate resources of his undermanned force during this extraordinary crisis.

Many other implausibilities and inconsistencies crop up, but the biggest flaw seems the absence of any real urgency on Howser’s part. It’s hard to imagine that even a veteran cop wouldn’t be more agitated over such a lurid set of circumstances.

In trying to combine the qualities of a mainstream novel with the contours of a thriller, it would seem, “Down by the River” fails to satisfy as either. The interactions of Howser and Crockett and some others, and what we learn about their lives, is interesting and well told in its own right, but it doesn’t seem to connect with the rest of the book. And the explanation of all the murderous doings, once it comes, is pretty far-fetched. Not even Howser can follow it, begging off with such lines as, “Hard to say. I’m no psychiatrist. . . . Yeah, it’s crazy, I know, but. . . . That’s just a guess. Who really knows? We got lucky.”

There is much to admire in “Down by the River”--a good command of prose, a nice sense of place, realistic major and minor characters. It’s too bad there isn’t more logic behind its excessive shocks. As it is, this horrific tapestry of small-town violence leaves far too many loose ends dangling in the stifling summer air.