Larry Quinn must die.

He's dying anyway, by torturous increments, of multiple sclerosis. So why shouldn't his best friend, Chris MacKensie, who is in love with Larry's wife, just put him out of his misery, thus killing two birds with one duck-hunting trip to Canada?

That's the promising if melodramatic premise of "The Love Hunter," in which "The Postman Always Rings Twice" meets "Deliverance" among the mucky fens of Manitoba. Minnesota professor Jon Hassler, whose first two novels, "Staggerford" and "Simon's Night," were modest successes, has set his sights high for this eternal triangle. And when in the end he misses the mark, it is not for want of invention.

Hassler is a skillful plotter with a good, strong story in the voyage of Chris and Larry -- faculty colleagues at a college in Rookery, Minn. -- to Blackie LaVoi's hunting camp in the lonely marshes near Winnipeg. The sporting sequences are loaded with intriguing subsidiary characters: aging guide Blackie LaVoi (an irascible dipso with a face "the color of duck meat" who can prattle for hours about "bear hide and goosedown, moose meat and venison"); and his slatternly sidekicks, Gladdy and Poo Poo, two pliable bimbos who staff the camp and double as $30 hookers.

The author's capacity for physical description can be impressive, especially when he recounts the grinding anguish of Larry's progressive deterioration, the masculine rituals of the hunt and the sudden bloody violence that climaxes the action. When Hassler is working this territory, his prose is clean and evocative, his plot-twists graceful and his narrative talent abundant. Unhappily, those scenes make up only half the book. The other half is the 18-year history of Chris' developing romance with Larry's wife, Rachel, and his evolving decision to murder Larry out of mercy. This story, told by flashbacks in alternating chapters, lacks the power and authenticity of the hunting sections, and is often frankly incredible.

The first warning comes in the hollow clatter of women's-magazine language, whether describing Rachel with her "blood-red nails," "slim legs" and "pert rump" ("In the sun she was radiant. She, too, pierced Chris' heart . . . he was shot through with joy") or Chris' feelings about killing Larry ("bristling with apprehension, horrified at the thought of murder"). This kind of prose does for fiction what food coloring does for bologna, but it is merely symptomatic of some larger misjudgments.

Hassler seems not to understand the character of Rachel, a talented actress whose enforced devotion to Larry is as debilitating as his illness. And he assumes that a generous reader will take for granted the kind of Grand Passion that will drive a blandly competent academic like Chris to contemplate actions that make J.R. Ewing look like Beaver Cleaver. But Chris simply never develops those dimensions, and the reader is never shown his passion, only told of it in baffling emotional shorthand or inhuman dialogue like that in this scene:

" 'Be strong,' he told her downstairs, at the door to the parking lot.

" 'Say it again.' Her smile intensified his ache.

" 'Be strong.'

" 'And once more.' She laughed a short laugh to cover her need.

" 'Be strong.'

" 'I know it sounds dumb, but it helps to hear that. Your voice has a healing effect. I may come back again to hear you say, 'Be strong.' "

Hold on to your heart medicine, Beatrice, there's more: This bewilderingly inane exchange provokes Chris to decide "insofar as one can decide such a thing -- that he was in love. What he felt for this woman was more than delight. Delight was fleeting and fun. This was a throbbing that warmed his brow and breast like a fever, a wound."

Hot enough for ya?

Chris' shallowness of soul is the more surprising because Larry Quinn is a fully realized character whose feelings and behavior Hassler has worked hard to imagine. Partly by design, we gain in understanding and empathy for him as our patience with Chris' tepid little adulterous motives runs out.

Despite its shortcomings, however, "The Love Hunter" reveals its author to be a generally skillful marksman. If he finds the right target in his next book, he could bring home quite a trophy.