Mrs. Demming and the Mythical Beast by Faith Sullivan (Macmillan: $16.95; 341 pp.)

Larissa Demming, 47, mother of two grown children and wife of a terminally distracted academic and writer, Bart, seeks solace at her Minnesota summer home by packing a picnic and reading a mystery, “Murder at Montmorency.”

“When I feel unsettled,” she tells us, “a mystery in which sophisticated, chatty Londoners motor down to someone’s place in the country for a fatal house party usually settles me.” And at first, “Mrs. Demming and the Mythical Beast” promises to be just that--chatty, filled with stock characters and pleasant settings, and just enough plot to keep you going.

But Faith Sullivan packed her story too full of family conflict, crumbling marriages, environmental fights (rotten developers from Texas, no less), incest, and the beast of the title. Had it worked, the novel would have been John Fowles plus Oedipus Rex. It is pleasant enough in parts, but when the writer tries to have it both ways--fantastical and realistic--the work dies from too much exposition.

As the book unfolds, Larissa realizes that she can’t stand her husband, that she is in love with her friend Harry, that her daughter finds her insufferable.

She invents or comes upon Pan, who bears a strong resemblance to her long-lost father, with whom she’d had an affair after her mother’s death. Pan was brought to the Belle Riviere River by a young heiress more than 90 years before. Larissa decides to return him to his native Greece.

The beast, who must bear much of the symbolic and plot burden of the novel, is not a success, either as a realistic or a magical figure. He seems like someone it would be all right to picnic with--but not the son of Hermes, not an immortal who has survived Minnesota winters with his memories and a copy of “Huckleberry Finn.”

As in the kind of novel Larissa might want to read, everything gets settled in “Mrs. Demming and the Mythical Beast.” Pan (who has been troubled by a mysterious white hound) disappears when Larissa’s father--the real mythical beast--appears in Greece. Larissa makes peace with him before he dies. Bart falls in love with a waif, so Larissa can leave him without guilt. Larissa’s artwork becomes the hit of the Midwestern art world. Bart’s novel about ancient India becomes a best seller. Larissa gets to be with Harry.

Unfortunately here, the dramatic and the tidy, in the absence of believable characters and compelling situations, don’t satisfy.