THE CLASSIC BRITISH MYSTERY is, more than anything else, a state of mind. Once the susceptible reader knows how it feels, he searches for the same sensation over and over again. Each of its elements is so familiar that the chief inspector sent to investigate the murder in P.D. James' ninth novel, The Skull Beneath the Skin, remarks that he regards the butler on the premises at the scene of the crime as a "gratuitous insult on the part of fate." It's an in-joke, just like the title of Edmund Wilson's infamous essay on the genre, "Who Cares Who Killed Roger Ackroyd?" or any reference to a dog that does nothing in the nighttime. James, who began her career with all the fanfare given to a Margaret Yorke or Margaret Erskine, to an Elizabeth Ferrars or Elizabeth Lemarchand -- namely, none -- now finds herself shouldering the ermine cape and wielding the scepter. Twenty years after her first book, Cover Her Face, appeared, she's become the new queen of crime. For addicts, P.D. James is the drug of choice.

However, Agatha Christie she's not, even if she appropriates, as she does here, characters, etc., that in their naked state Christie would certainly recognize. James' aging yet still beautiful and very narcissistic actress, Clarissa Lisle, and her ex-military, too-tolerant husband, Sir George Ralston, for example, can be found wearing other identities in Christie's Evil Under the Sun. Or the island setting, the prototypical closed community which plays such a large part in the classic school: here off the Dorset coast and called Courcy Island, in Christie's Ten Little Indians, it was near the Devon coast and named Indian Island. Or what about the event that draws the characters (victim, suspects, sleuth) to this relatively isolated place? It's an elaborate amateur production of Webster's The Duchess of Malfi, to star Clarissa Lisle, who, unfortunately, is killed before the curtain rises. In Michael Innes' Hamlet, Revenge! a similar theatrical occasion provided an opportunity for murder.

No, James is not particularly original this time out and her fans must be grateful for it. More Innes-like (he's the star practitioner of the so-called donnish, erudite style of mystery- writing) than Christie-ish, she is given to having her characters speak and think in literary quotations. Though no one in life does that, everyone in The Skull Beneath the Skin does, from the police sergeant to the butler. The title itself, in a twisty double-play, is taken from a T.S. Eliot poem which alludes to Webster, who is, you'll remember, the author of the play being rehearsed by the doomed Miss Lisle. Yet, although she shares this affinity for the words of others with Michael Innes, James lacks his strong vein of whimsy, his pleasure in learned slapstick. Somewhat prim and serious, like her heroine, detective Cordelia Gray, and bearing the weight of her own intellect and relentless good taste, P.D. James is all brains and no flair.

Cordelia is making her first appearance since her debut in the critically praised An Unsuitable Job for a Woman in 1973. "Bring back Cordelia!" went the cries throughout the '70s. (Accompanying those noises were pleas that James also allow Cordelia to have a love affair with James' recurring hero, "poet-detective Adam Dalgleish of New Scotland Yard.") And so James has done, but Cordelia is less appealing than she was 10 years ago. Then she was refreshing because of her vulnerability. With a clear head and spirit, she was neither hard- nor soft-boiled, not a caricature of the male detective. The private investigation agency that she had fallen heir to was called Pryde's and the name seemed particularly apt. The way people age in book series is not the way they do off the page; many fictional characters never change at all. But Cordelia, who seemed very, very real -- despite An Unsuitable Job's perfectly outlandish plot -- has not fulfilled her potential for growth. In 1982 she seems limp, a bit of a sad sack. She's the same outsider she always was, which is, in fact, the perfect position for a woman detective, heightening as it does her awareness. But her vulnerability is now close to self-pity. James, I think, means for Cordelia to be a complex figure, but she's starting to remind me of St. Joan: noble and courageous and listening to the wrong voices.

Having praised P.D. James in the past-- most notably in 1973 when she published An Unsuitable Job for a Woman--and watched her ascend to the throne, I now have to confess to mixed emotions about a writer who is admirable in so many ways. Greeting each of her books with pleasant anticipation, I have not enjoyed those that followed An Unsuitable Job: The Black Tower in 1975, Death of an Expert Witness in 1977 and Innocent Blood in 1980. I wanted to; I tried. Finally, I grew to realize that P.D. James is just a little bit too stolid for my taste. When she tries to portray eccentricity, as she did in The Black Tower or as she does in The Skull Beneath the Skin, with its Victorian fantasy castle, she simply -- for me -- falls flat. Far better were two of her early titles, A Mind to Murder (1963) and Shroud for a Nightingale (1971), when James, a hospital administrator-turned-Home Office senior civil servant, poked around amidst the medical surroundings she knows best. In Death of an Expert Witness, too, one felt James to be more at home among the forensic scientists she portrayed. And Innocent Blood, although an emotional and rather lurid story, was bloodless.

Perhaps it was a mistake for James to choose the mystery genre as her venue of authorship. She has said that she did so because "I thought I might be able to write a mystery rather well" and that "I reasoned that such a popular genre might have the best chance of acceptance by a publisher." Acknowledging her own love of mysteries, especially Dorothy L. Sayers', she also stated that the mystery's "challenging disciplines, its inner tensions . . . and its necessary reliance on structure and form (were) the best possible apprenticeship for a serious novelist."

Although claims are continually being made that she has "revitalized" mystery writing, I think that James, having served her apprenticeship long ago, has for a decade now only been going through the motions. Innocent Blood was her "breakaway" book, and, as far as sales went, it did. So why can't she now bid farewell to the mystery story and break further away? There's a feeling of pandering in The Skull Beneath the Skin, of giving her audience what they want and expect; there's even a sense of parody there, lurking deep under the text -- the skill beneath the skin, as it were. Her heart's just not in it.