JOAN AIKEN IS SO COMPETENT and experienced a writer, so sure of her language, her characters, her situations, that often it seems this should be enough, that the reader should and could ask for nothing more. These 15 stories, some of which have been published separately in England at various times over the last 20 years, are all together here for the first time, and they are as competent as should be expected; smooth, strong, sure writing, and a varied meal of moods. None of them particularly lingers in the imagination after the book is closed, none reflects the dismal brilliance of a genuinely macabre imagination, and yet they are very good.

They do not, any of them, go in much for the blood and gore that passes for horror in the movies these days, nor do any of them deal flat-out with the supernatural, also a common movie gimmick. Rather they run on the gray edge between order and chaos called so aptly the "twilight zone" by the old television series. A mother and son, driven to despair by a nagging, unfeeling husband-father, turn themselves into trees. A black box has the power to destroy life. An unlovable teen-ager is wooed to a half-life in a ruined mansion by a Miss Havisham-type old woman. A town that is a Brigadoon-like paradise is found, lost, found again by a storm-tossed sailor.

Some are lighter: A little girl has living in her hair an entire tribe of ancient Gauls displaced by the Romans centuries ago. A buyer for a London firm finds a diamond-bearing elephant in the Balkans. A shipwrecked woman encounters highly intelligent mice who lead her to salvation. Some are tragic: A doomed child fears the upstairs because she will die soon on a second floor. A lonely man is kept on the fringes of life and action by his fear of involvement. And one, the least successful, is rather more science fiction, wherein the world is taken over by invaders from another planet. And everywhere, living or dead, nice or not so nice, there are cats.

What Aiken may lack of the aforementioned macabre imagination she makes up for to some degree by her mastery of scene setting and characterization. Throughout these stories, whatever their degree of success as suspenseful tales, the people seem real and move through beautifully detailed, evocative worlds both commonplace and bizarre. Aiken describes with equal skill the feel of a ship crowded to the gunnels with immigrants, and a dark house on a lonely moor. The reader feels she must have seen and known them all, that nothing is invented.

Yet, in spite of the author's skill, one comes away finally untouched, and it is extremely difficult to say why. There are ghost stories, read recently or long ago, that live on and on in the memory, never losing their power to raise gooseflesh. I wonder if these stories must not spring from minds that are bruised somewhere, that comes to the edge of madness insofar as they seem thoroughly to believe, themselves, in the stories they tell -- that they are haunted, themselves, and write for their own relief rather than to entertain a prospective reader. Perhaps an author must be himself struck with horror, to transmit that horror effectively to the reader. Poe's "The Tell-Tale Heart" is unforgettable. Even his poor old "Raven" still has the power to chill. There is a northwoods tale called "The Wendigo" (author unknown to me) that I would dearly love to forget. Coleridge's "caverns measureless to man" and even the lonely sea of his "Ancient Mariner" are permanent parts of the gloomy landscape of nightmares. And our own nightmares, swimming up from Heaven knows where, can leave us terrified.

Joan Aiken is perhaps too literate, and too sane, to bring this kind of story off supremely well. True horror has no sense of humor, that crowning attribute of sanity. Though Poe and his fellows were certainly gifted writers, their work seems to have rushed full-blown and shuddering from its dark inspirations; one would never think first of competence with them as one does with Aiken in this collection. For though the reader feels she must have known her settings, that nothing in that area was invented, still there is a definite sense of invention in her gooseflesh, a sense of conscious craftsmanship, a sense of manipulation rather than participation. In short, Joan Aiken seems not to be on the edge of madness. And perhaps that is the final sieve separating the sweat of hard work from the sweat of horror, making the final all-important difference.

These are finely crafted stories, but they won't keep anyone awake. Maybe that is all to the good. We have more than enough already to keep us awake these nights.