"What are you," a colleague asks Dr. Hugh Welchman early in this intricately twisted novel, "a doctor or a blasted detective?"

Actually, Welchman is a bit of both -- that is to say, he is a psychiatrist, and his latest case requires him to search out the facts in the rather odd death of Arabella Brinton, 14 years ago. Arabella's son Alex, who was 5 when she died and is now an undergraduate at Cambridge, has come to Welchman with a curious psychiatric problem. "The truth is that I'm afraid of going downstairs," he tells Welchman with "an awkward little laugh" at their first interview. The phobia relates only to one particular stone staircase in the college where he lives, and he only has problems going down, not going up. But since he lives on the second floor, the phobia makes it hard for him to attend classes. At one point "he had been driven to climb out of the window and drop onto the flower bed below when no one was looking." To cure his patient's phobia, Welchman may have to solve an old crime -- if, in fact, there was a crime; on this, as on almost everthing in the case, the evidence is conflicting.

Slowly (nobody in town seems interested in immediately telling Welchman the whole truth), it emerges that Alex's mother died by falling down a flight of stone steps, that there is a serious question about whether the death was actually an accident, as the court records say it was, that Arabella was an alcoholic and a domestic tyrant who gave strong murder movtives to a variety of people. She was coming up from the cellar with a forbidden bottle of whisky when the fatal incident occurred. Fourteen years later, when another woman falls down another flight of stone steps, triggering Alex's phobia, he recalls that "the whole place smelled of whisky." He is mixing up one incident with another (at which, supposedly, he was not present). And he is evoking the memory of a mother whom he has completely blocked out of his consious mind, reserving the title of "mother" for the stepmother who followed rather quickly on the heels of Arabella and may have had something to do with her death.

If Julian Gloag were asked whether he is writing a psychological novel or a detective story, he would have to plead guilty on both counts. In addition, he is writing a novel about complex, sweaty and sometimes kinky social and sexual relationships in a small, British university town. The three main strands of his book come together with only an occasional bit of awkwardness because these three different ways of looking at the activities of the same set of people. In addition, like most good detective stories and most good psychological novels, "Sleeping Dogs Lie" turns out to be a really a novel about human perceptions and the nature of reality.

His conclusion about reality is hardly a new discovery, but it is a point on which one needs periodic reminders. Reality is slippery. If sleeping dogs do not exactly lie, they are frequently misleading. In the course of novel, nearly everyone who might have had a reason and an opportunity for pushing Arabella down those stone stairs confesses to the crime -- usually to shield someone else who might also have had a reason and an opportunity.

After a long, tangled investigation of what he thinks are other people's problems, Welchman discovers traumatically that reality is not only hard to find but intensely subjective; the mystery he had been tracking down with cool professional detachment comes to rest on his own doorstep.

While telling his intricate story of genteel violence and polite deception, Julian Gloag introduces a rich variety of characters, ranging from an American-born professor who tries to out-British his colleagues to a stolid but sharp and cagily suspicious small-town detective. They are finely drawn, as is the complex, inbred social structure in which they function.

Those who are looking for a fast-reading mystery to while away a few summer hours may find that Gloag has given them more than they bargained for, including a few plots twists beyond the normal quota. This is a book for the reader who wants a substantial novel with a mystery at its core.