There may be some question about the credibility of this narrative, since Satan the narrator is commonly known as the Prince of Lies--though he spends a good many pages denying this and other charges and is still doing so in the book's last sentence. It may be that some of the things alleged against him are fabrications, as he claims, but he is hardly the completely straightforward person he would have us believe. For one thing, it is not until page 57 that we discover that he is not only the primary subject of the story but the one telling it--and also the charming, intelligent, superbly modulated voice emerging from the strange computer built by brillant, insane Dr. Leo Szlyck of MIT.

The book's secondary subject is the unfortunate Dr. Kassler, who is relegated to the subtitle. By the time he begins to work on his distinguished patient, Kassler is no longer a doctor. Various accrediting agencies have discovered some compromising facts about his sex life and his professional conduct and, above all, the biographical footnote that he has spent some time in a mental institution, not as a doctor but as a patient.

The therapy was not an assignment that Kassler wanted, as Satan himself admits: "Kassler had about as much desire to treat Satan as I do to sing the Hallelujah Chorus, but, fortunately, when we finally got together, Kassler was at a point in his life where he had no doubts that I was real." As a matter of fact, Kassler has been through hell before he is driven to accept its proprietor as a patient. He has been manipulated shamelessly and painfully by Satan (with some necessary human assistance) to the point where he is ready to commit suicide, and he finally agrees to the treatment only because he wants some information that can be obtained in no other way. "What is life?" he asks Satan, having first been informed that that is The Great Question. A reviewer who revealed the answer would be cheating, no doubt, but it is probably fair to say that the answer is diabolical, and that some readers will find it anticlimactic if not untrue. Such disappointments are to be expected, no doubt, by those who dialogue with the Devil.

For that matter, the big answer to the questions that drive Satan into psychoanalysis is also a bit of an anticlimax. For most of the book, it seems that Satan's problems are not really psychological but social. He presents himself as the embodiment of pure reason, as opposed to the superstition, exploitation of fear, pretentious posturing and ill-temper that he attributes to the Other Side of the eternal polarity. What seems to bother him is not suppressed childhood memories but the simple question of why he was evicted from Heaven; why everyone says such bad things about him. Finally, at the end of the last session, Kassler uncovers the secret and cures his patient. By all the evidence, he is a good therapist, although he operates with a fraudulent degree and has made an incredibly complex mess of his personal life.

Why was Satan thrown out of Heaven? The answer dredged up by Kassler has the simplicity that usually lies at the core of the baroquely elaborate structures investigated in psychotherapy: "You were thrown out of heaven because you wanted to be an author . . . You wanted to write your own book, explain your side, tell your story." After pausing to let the revelation sink in, Satan agrees: "He's got two whole testaments. And a lot in between. What have I got? Nothing."

Well, now he has one book, at least, without going into the knotty questions of authorship in many other books that have been attributed to him and his minions. Besides an impassioned apologia and a harrowingly detailed account of his therapist's unfortunate life, the book has some very vivid incidents relating to the human reproductive process, some vivid descriptions of mad scientists at work, and a lot of psychological interest--abstract, textbook psychology and concrete psychology as it manifests itself in human behavior. Some of the book's most charming characters, as well as some of its worst, are nutty as fruitcakes. There are also fragmentary but interesting discussions of such weighty topics as entropy, artificial intelligence and unified field theory.

In sum, Satan has a long way to go before he can catch up with the human interest, wisdom, stylistic elegance and sales figures of his rival's book, which has been a perennial best seller since the invention of printing. But he is doing fairly well for a first novelist. Whatever that fellow Leven had to do with "Satan," he already has another novel, "Creator," to his credit.