Knife in the Water : THE WEIGHT OF WATER.<i> By Anita Shreve</i> .<i> Little, Brown: 256 pp., $22.95</i>

Anita Shreve is fascinated by crimes of passion, by what the journalist in her 1991 novel, “Strange Fits of Passion,” described as “the draw of the unnatural act unfolding naturally.” Once again, in her fifth novel, heinous crimes--incest and murder most foul--are presented in such a way as to heighten our sympathy for the perpetrator and make us question our moral certitudes. Once again, the author of “Eden Close” and “Where or When” tells her story by an outside researcher--this time, a photojournalist named Jean--who is pulled into the ambiguities of a supposedly locked-up case and haunted by the details she unearths. “I have to let this story go,” Jean says at the beginning of “The Weight of Water.” “It is with me all the time now, a terrible weight.”

Set on the Isles of Shoals 10 miles off the Portsmouth, N.H., coast, “The Weight of Water” tells how a magazine assignment to do a photo essay about the 19th century murder of two Norwegian immigrants, Anethe and Karen Christiansen, changes Jean’s life. The murders really did take place on the island of Smuttynose in 1873, and the trial that resulted in the conviction and hanging of fisherman Louis Wagner was called “the trial of the century.” Now, the magazine editor wants to tie in the Smuttynose murders with the unfolding “trial of the century,” an oblique reference, I assume, to the O.J. Simpson murder trial.

Jean enlists her 37-year-old brother-in-law, Rich, and his Morgan 41, a sloop, for the project. Along for the ride are Rich’s sexy new Irish girlfriend, Adaline; his older brother, Thomas, who is Jean’s husband of 15 years; and their 5-year-old daughter, Billie. Thomas is a prize-winning poet, but he is hard-drinking, deeply tormented and often blocked. Adaline’s presence is the spark in the mix, particularly as Jean begins to suspect an affair between her and Thomas. Lines of quoted poetry fly back and forth between Thomas and Adaline like “pingpong balls hit hard across a table”--a private language between them that heightens Jean’s growing sense of exclusion.

Shreve captures the pervasive dampness and claustrophobia of tight quarters on board the small, rocking craft with shimmering prose; there is a sense of foreboding from the first page. Smuttynose, the backdrop to Shreve’s tale, is a barren island of “sere and bleak” granite with “jagged reefs that cut.” Shreve’s sharp descriptions depict a landscape as raw and gloomy as any to be found in the books of Thomas Hardy.

One of Shreve’s favorite tricks, also used in her previous novels, though never quite so effectively, is to integrate various “source” materials into her narrative to lend it historical weight and depth--trial transcripts, letters, a found document. In “The Weight of Water” she creates a handwritten account of the murders penned by the sole survivor of the attacks, who hid in a sea cave until dawn.

Twenty-six years later, alone and dying back in her native Lauvig, Maren Hontvedt seeks to “unburden” herself by writing about that grim March night on Smuttynose when her sister and sister-in-law breathed their last. Jean snitches this overlooked document and its translation from an uncataloged library collection in Portsmouth because she wants “to find the one underlying detail that will make it all sensible.”

Maren’s document enables Shreve to tack back and forth between her 19th century story and her modern one. Only occasionally does a hint of 20th century sensibility creep into Maren’s narrative. For the most part, however, Shreve navigates deftly from one distinct voice to the other like a boat that is constantly jibing but still heading on course. Parallels between the two tales are made apparent without being run up the mast. The technique works because the two stories are equally gripping and because we feel that a capable captain is at the helm.

Maren’s story tells of “the uncommon love” she bore her brother Evan and “of how my life was shaped by this devotion.” As in Jeanette Haien’s quiet little morality tale, “The All of It,” incest is treated with delicacy and complexity. Maren’s much older sister, Karen, a sour person about whom Maren professes ambivalence, picks up on this “unnatural love” and regards Maren forever after with suspicion. Maren reluctantly marries her brother’s employer, John Hontvedt, who brings her to America. They settle on Smuttynose, a suitably harsh site for their barren marriage. Within a few years, they are joined by John’s brother Matthew, an ever-embittered Karen and, finally, Evan and his lovely new bride, Anethe. Shreve deftly conjures the stale “fetid atmosphere” of six adults shut in day in and day out in a tiny sealed cottage during the cold winter months, a fitting parallel for the caged closeness on the Morgan 41.

Both stories build inexorably to their drastic, deadly and somewhat unexpected climaxes. Maren cannot move beyond her tortured, improper love for her brother, as he so clearly has with his affable wife Anethe. Nasty, righteous Karen tries to rub in Evan’s indifference. Jean watches Thomas and Adaline warily. Then, a perilous storm hits the Morgan. Jean, who thought of her years with Thomas “as a tightly knotted fisherman’s net,” is stunned to find that “in the space of time it takes for a wave to wash over a boat deck,” the net has frayed beyond use. The speed with which lives unravel is at the heart of both strands of Shreve’s stunning tale. There is plenty for the reader to ponder and savor in this accomplished inquiry into the ravages of love.