When James Laver was curator emeritus at the Victoria and Albert Museum, he remarked that one factor that made dating historical paintings relatively easy was the reluctance of the person painted in period costume to conform to an earlier age's idea of beauty. A Victorian lady might choose to be pictured in the costume of the Elizabethan court, but she was not willing to shave her hair back off her forehead.

Something similar happens in historical novels. The heroine may be dressed in the clothes and customs of the time, but invariably she is suited up with a modern sensibility. And so Thomazine Heron, the heroine of "The Moon in the Water," a story set in the mid-17th century, has been given the traits most likely to appeal to a woman of the 1980s. Thomazine is an independent woman, as liberated as That Cosmopolitan Girl.

From the moment she first appears -- a 10-year-old orphaned heiress being delivered into the hands of her Suffolk cousins -- Thomazine rejects the limitations that society puts on females. Although she learns to sew and play the lute, she also insists on joining the boys at their Latin and Greek. Cousin Lucy dreams of romance; Thomazine climbs trees.

This is not the behavior expected of a Heron, for they are important people, so rich with possessions and the retainers to care for them that

The reviewer is the coauthor of "The Lessons of Love." when Thomazine asks a cousin whether he was seen sneaking from his room, he responds in surprise: "Think, child. This place is crawling with people like maggots on cheese . . . It is impossible to go from here to the library and back without being seen by at least one of the sixty-odd people who live here."

They are also a large enough family to provide a good deal of drama. There is Simon, eldest and most righteous of the Heron children; Edward, the good-natured soldier; Francis, the imaginative rebel; Lucy, the dreamer; and Jamie, the baby who is afraid that by the time he gets big enough to do anything there won't be anything left to do. Add a set of Scots cousins, and the Cornwall cousins, and the Yorkshire cousins, and a tangle of neighbors, babies, horses and dogs, all wandering around a country divided by Civil War.

Unlike the traditional historical heroine, who can tell a villain by the cut of his cloak, Thomazine is never quite sure about her enemies. No sooner does she call out their perfidy then she begins to waver, wondering if perhaps the fault lies with an unhappy childhood when their natures got no nurture.

If all this gives a slightly modern cast to the characters, they nevertheless speak in the dialect of their period, eat endless bowls of frumenty (a porridge-like concoction), perform for each other from the plays and poems of the time, play bowls, and when they do go to war, their weapons are shot and cannon, so that observers can take to a high hill and watch the fighting down below: "The smoke, from cannons or muskets, obscured much, but I could see clearly the great tangled mass of foot-soldiers struggling perhaps half a mile or more away . . . Faintly, far off above the gentle rush and rustle of the wind in the grass, came to our ears the cries and crashes of the battle. It was an experience at once beautiful and terrible in its implications, that we could watch rampant death thus calmly, as if at a play."

As the war takes a life here, disrupts another there, Thomazine moves from Suffolk to Oxford to Scotland -- caught by battle, caught by siege, but always in pursuit of Francis, the cousin she loves, for "The Moon in the Water" is primarily their love story as these two find each other and lose each other and find each other and lose each other.

Despite their efforts, they remain apart and the book ends with Thomazine setting out one more time in quest of Francis: "As we rode through the empty, half-lit, golden streets of Oxford in the dim morning, my heart was light and hopeful, and my eyes strained towards the welcoming North; for at last I was going to Francis."

But wait! No publisher could be that mean, so a month after the release of "The Moon in the Water," Berkley issued a sequel, "The Chains of Fate." Wherein the lovers are reunited in Scotland, and separated, and reunited again, and . . . it is beginning to seem awfully familiar and a bit tedious, because while "The Moon in the Water," all 530 pages of it, is fun to read, with its endless crises and its lutes and love poems and unicorns and castles, the story does not really sustain a whole other book.

Thomazine's focus is always on Francis and Francis is simply not that interesting, more a device used to push Thomazine out into more adventures than a person with depth of his own. By the end of "The Chains of Fate" you want to grab hold of Francis and Thomazine, give them a shake and tell them to please, for heaven's sake, get on with it.