Here Christopher Isherwood continues to perform open-heart surgery on himself, without anesthetic, and with one beady eye on the audience. Readers of the magnificent first volume of the Diaries (1996) will know what to expect. Those who missed out are in for a rare treat: Isherwood is only as vain, as venomous and as near-sighted as any other honest-to-goodness diarist, but with one crucial difference. He can write.

By the 1960s Isherwood is living in Santa Monica, is famous, rich  though not yet rich enough to give up teaching  and remains devoted to his California-Indian guru Swami Prabhavananda. He is also weathering the endless storms of his relationship with the artist Don Bachardy, 30 years his junior, with whom he is engaged in continual "psychological wrestling matches". Among other things, the Diaries serve as a prime ringside seat for grapple fans.

During the 60s, Isherwood appeared to be  and in many ways was  the quintessential expat Brit about town. There are plenty of parties, dinners and soirees. He is out one night with the King Vidors, and then out another with Nehru, or Marlon Brando, or Danny Kaye. When he throws a party for a few close friends, it's Aldous Huxley, Alec Guinness and his wife, and the Stravinskys. He goes on a trip to see Cecil Beaton; goes on TV with Arnold Wesker; has dinner with a young Alan Bennett ("quite shy, with a non-U accent"). He meets Joan Littlewood ("a pretty bogus down-to-earther") and Timothy Leary ("He really is a fake"). Then pops round to Kenneth Tynan's to watch Tynan's new TV show, does a quick bit of pall-bearing at David Selznick's funeral, has drinks with Freddy Ashton, and enjoys an afternoon on a "famed fag beach" with Wayne Sleep.

Given his hectic social schedule it's difficult to see how Isherwood could ever have done any work at all. And a lot of the time he couldn't  too pissed, too tired, and then too much time in the gym. The social life not only took its toll but was in itself unsatisfactory. "Drinking, idling, wasting time with people I didn't really want to see; and getting nearly nothing done on the novel," he complains in November 1960. When he does knuckle down he wastes his time giving lectures and spouting nonsense. On 10 October 1960 he writes: "The week after this one will be particularly tough: my lecture on 'The Nerve of the Novel', which is probably the most difficult of the whole lot. A possible appearance on local TV; God knows what I'll say. And then, next day, a luncheon speech on 'Writing  A Profession or a Way of Life?'" No wonder that by February 1961 he is yelling to himself, "BUT I MUST GET ON WITH MY WORK."

The diaries are his work. What is emerging in these vast volumes, scrupulously edited by Katherine Bucknell, with presumably at least one more to come  Isherwood didn't die until 1986  is one of the great literary accounts of the 20th century. Of course, one doesn't necessarily turn to Isherwood for profound discussion of the great matters of public life and politics, but one does go to him to find the strange effects of politics upon the private life. During the Cuban missile crisis he writes: "I feel such a curiously strong loathing of Castro  something to do with his beard, his sincere, liquid-eyed beard. I should like to see him forcibly shaved in the UN." Like the rest of us, Isherwood lives half the time in the world, the other half in fantasy.

In many ways, he was at the vanguard of social change throughout the period. After a dinner party with colleagues in May 1962 he writes: "Sure, I am prejudiced, but I feel always more strongly how ignoble marriage usually is. How it drags down and shackles and degrades." His own idea of a good night in is quite different. "Everybody got high, and Ginsberg recorded our conversation and chanted Hindu chants, and Orlovsky . . . kept asking me if I ever raped anyone, and the boy Stephen unrolled a picture scroll he had made, under the influence of something or other, to illustrate the Bardo Thodol [the Tibetan Book of the Dead]."

There is more telling domestic detail in one entry in the diaries than in an entire episode of Mad Men. He trips over a barbecue pit. He tries the Calories Don't Count diet. He has the typewriter serviced. He watches Japanese porn films. And he is casually anti-semitic. Actually  alas  maybe he's not so casual about it. Reading Paul Goodman's Making Do in July 1965, he remarks that Goodman "redeems single-handed the drivel of the other Jews". In November 1966 he doesn't go to see the play of Cabaret in New York because "It sounds Jewish beyond all belief". In 1961, when some representatives from UCLA ask him to give some lectures, he is appalled that they try to negotiate with him over the fee. "Whatever anyone says, this kind of thing nauseates me; it is Jewy and vile and utterly shameful, coming from the representative of a serious institution of learning instead of an old clothes dealer." And this, coming from a serious writer instead of an old hate-monger. It's an ugly blind spot, in a book of otherwise quite beautiful blind spots.