THIS IS ONE of those historical novels of romantic suspense that sinks under the weight of its melodrama. It is loaded with dark, enigmatic secrets. What, for example, has caused the unhappy shadow that lies behind the fine eyes of handsome Sir John Devenish? Why does his wife, the fragile Lady Iris, take tincture of laudanum? What is wrong with their daughter, Celina, whose strange beauty is distorted by her eerie silences? And, above all, why are the Devenishes, an important British family, closing up their county estate and London town house to emigrate to a colonial backwater like New Zealand in the year of Our Lord 1862?

These questions gnaw away at our heroine, Kate O'Connor, but despite her forebodings and misgivings, she takes the job as companion to Lady Iris and Celina on their trip to the Canterbury Colony. The plot meanders, dawdles and drifts along as the family settles in at Avalon, a sheep ranch. They meet other settlers, mix into the upper echelons of Christchurch, and Kate develops a romantic interest in a certain Captain Oxford, only to have him stolen away by Celina. Kate's disappointment, however, is blunted by a far more dangerous attraction. Lady Iris, nearing 40 and not entirely of this world, is no match for her virile husband, and when Lord John casts an eye in Kate's direction, she discovers to her horror that she is not impervious. At this point the plot, as they say in the vernacular, thickens and all dark secrets are revealed after a sufficient interlude of murder and mayhem.

Readers of historical suspense are going to be disappointed in this latest book by a prolific and well-known author. The main plot lacks credibility and the subplots are weak. The pace is ho-hum in some spots and a race to the finish in others. There is so little depth to the characters that they remain, for the most part, shallow and one-sided. I didn't really care what happened to Kate O'Connor or the Devenishes. Nor, I suspect, will other readers.