THESE TWO NOVELS pretty well define witchery, and several other poles as well, including craftsmanship. On the one hand, The River Witches is trick-or-treat candy tumbled cheerfully into a bowl without regard for anything but the sweet tooth, while The Devil on the Road is a full, well-planned meal to be eaten when there's time to linger over it.

Robert Westall has written a well-researched account of witch-hunting in 17th-century England. The story is one of those in which a person from today goes backward into the past. It's a complex plot, hard to encapsulate, but the gist is that John Webster, a British teenager, finds himself living in an old barn owned by Dered Pooley, a farmer whose family has been in the area for centuries. Little by little John is drawn into Derek's effort to revenge the ravages of Matthew Hopkins, a real 17th-century witch-finder who brought about the execution of hundreds of women.

There are always problems with time travels which involve real histories, and The Devil on the Road does not escape them, though Westall handles the transitions with great subtlety and skill. But the writing is so charged and vigorous, the timing of the plot so carefully measured, that the customaray difficulties are minimized.

John Webster seems very real indeed, and likable; and even better, there is a young cat, deeply involved in the story and central to it, who is surely one of the best and most charmingly drawn cats I've ever encountered in a book. Her presence in the story does for it what real cats can do for real life -- she is all animal but still profoundly enigmatic, a creature of many wisdoms, a link between the known and the unknown. As such she epitomizes the story itself in all of its convolutions. The author is to be congratulated on a superb characterization here.

Without the cat and John Webster's hard-edged, vivid voice, The Devil on the Road would be just one more in terms of suspension of disbelief. And for this reader, at any rate, the book's final section, in which a group of characters from the past cross back into the present with John, allows disbelief to drop down again with a clulnk. For me, the shape of the novel is damaged hereby, and the fragility of the premise fatally exposed.

But American teenagers ought to enjoy this story very much and identify easily with John in spite of his British idioms. He is blessedly three-dimensional and therefore more than welcome in a field where two-legged stools have been letting everybody down long enough.

At the other extreme, it is my painful duty to suggest that The River Witches, though long on high spirits (pun intended), is rather short everywhere else. It characters are as various and full of energy as the sweets, in that trick-or-treat bowl, but they don't hang together, are poorly developed and keep changing their flavors.

Our hero, Andrew, is sent across the river, ostensibly to help his Auntie Lizard run her apothecary shop, but she's not really his aunt and he dislikes her intensely. Auntie Lizard is darkly sinister, as is her cohort, Ashton Dansforth, but the pair turn out to be good witches, somehow or other, though their plans for Andrew are not exactly benevolent. It is Miss Celestial Grace who is the real baddie. She wishes -- oh, horrors! -- to devise a spell which will prevent everyone from knowing how to read and write, but she is foiled by Andrew. A necessary thing, of course, but a spell like that scarcely tingles the spine -- bad as it would be in real life -- and its foiling comes well before its flowering, eliminating tension and further enfeebling the story line.

The problems are numerous in this novel. Its frequently stubby sentences rob the prose of music, and it glides merrily over time difficulties: for example, a storm during a ferry crossing seems to last about an hour but turns out to have taken an entire night. Strict observance of many kinds of facts are essential to good fantasy. Crises loom, then dwindle away pointlessly. Expectations are raised for horrors which never materialize. In short, it is slipshod.

It's clear from flashes throughout that Schecter is perfectly able to write with real wit and insight. One can only hope that he was distracted when writing this, rather than that he doesn't respect his audience. Nevertheless, some children may well get a kick out of this book, if only because of its broad, good-natured jack-o-lantern silliness.