Henry James thought Oxford the finest thing in England. This was before the place became a mini-Detroit, the home of British Leyland, where ceaseless lorry traffic rumbles past Matthew Arnold's dreaming spires "whispering the last blandishments of the Middle Ages." Modern visitors are unmoved by the whispering until they pass through college gatehouses into Auden's "quadrangles where Wisdom honours herself . . . promising to the sharp sword all the glittering prizes."

Oxford's magic is composed of legendary past, ancient architecture and academic grandeur -- a highly seductive combination of wealth, worldly influence and intellectual brilliance, inhabited by pampered individuals of apparently inexhaustible eccentricity.

This splendid world within a world is nowadays the literary province of J. I. M. Stewart. "Full Term" is the final volume in his autobiographical quintet of novels, "A Staircase in Surrey." The series is a celebration of Oxford, equal in entertainment to the 12 volumes of Anthony Powell's "A Dance to the Music of Time" and within the genre of Oxford novels the funniest since Evelyn Waugh's "Brideshead revisited."

Stewart also writes under the name of Michael Innes, and he is perhaps best known in America as the author of countless Inspector John Appleby mysteries. But he is in fact Professor Stewart of Christ Church College, Oxford, whose "Eight Modern Writers," the penultimate volume in the "Oxford History of English Literature," is a dazzling introduction to the Anglo-Irish strain in literary high modernism.

"A Staircase in Surrey" relates the adventures of Duncan Pattullo, a London playwright who returns to Oxford in middle age to take up a teaching fellowship at his old college. The series title refers to the entryway off a mythical quadrangle in the unnamed college where Pattullo has roomed man and boy.

Previous volumes in the quintet were "The Gaudy," "Young Pattullo," "A Memorial Service" and "The Madonna of the Astrolabe." They contain a progression of characteristic Oxford rumpuses and escapades whose linking thread is Pattullo's nostalgia for his undergraudate youth and the diffidence and uncertainty of his middle age. A gallery of Oxford types is lovingly presented: senile dons, suicidal students, alienated radicals, aquaphobic Australians, sprigs of the aristocracy and embattled faculty wives. Additional hilarity is presented in flashbacks to Pattullo's childhood in pre-Jean Brodie Edinburgh. Oxford's climate "(le rheumatisme vert," said Alphonse Daudet) is beautifully evoked, and the academic terms come and go, each with a new scandal or new permutation of an old. The university's outward face changes with the garb and sexual mores of undergraduates, but within senior common rooms and master's lodges Oxford remains Oxford, unchanging and ageless.

Part of the fun in all this is in deciphering the true identity of some of the characters. Pattullo's spectacularly absent-minded tutor J. B. Timbermill -- could he be J. R. R. Tolkien? Other allusions to Oxonians past and present, from Beerbohm to Iris Murdoch, are cunningly folded into Pattullo's story. Surrey itself seems a thinly disguised Peckwater Quadrangle, whose architectural good manners adorn Christ Church College.

"Full Term" ties up the loose ends of the eariler volumes in the quintet, including Pattullo's courtship of a second cousin. Her contemptuous treatment of Pattullo is caused by her ill-founded belief that he is actually her illegitimate father. She is set straight, and Pattullo recovers at High Table over the port. There is other tea-time gossip: the eminent nuclear physicist Watershute has abandoned wife and son for the fleshpots of Venice, or is it that he is a Russian spy?

At age 73, Stewart shows no sign of losing control over a very wellbred, belletristic prose style. He once wrote a spy novel in which secret orders were given in an invented stanza to Swinburne's "Forsaken Garden," sent to a literary supplement in a letter that asked "readers to enlighten me on the authorship of the following lines." The poem led to a missing mathematician, an orgy of transvestism in the Scottish Highlands, a hornet's nest of spies and a secret formula hidden in a collection of Caravaggios.

There is much of this kind of elegant teasing in "A Staircase in Surrey" -- it is simply delightful -- but there is also the graceful thanks of a man who knows he has been privileged to spend half a century in the most ivory of towers.