The widows of Eastwick contains witches and spells, but like its 1984 predecessor, The Witches of Eastwick, resists crossing over into the category of the paranormal. It holds on firmly to dual nationality, unlike the film version of the earlier book, which crossed over fairly crassly - but genre in books is much more flexible than in films. Or it can be, if writers care to exploit the possibility. The key is to avoid the pace of a thriller, never a problem with a prose as quietly rich as John Updike's, and a strategy adopted with success by Hilary Mantel in her splendid Beyond Black.

In The Widows of Eastwick the three retired witches, widely separated in space, have lost husbands who were real men with their own histories, virtues and limitations, and at the same time had been magically conjured by their wives. Alexandra, for instance, cooked up her lovely husband Jim, a lean taciturn potter with a limp, from a hollowed pumpkin, a cowboy hat and 'a pinch of Western soil scraped from inside the back fender of a pick-up truck with Colorado plates'. But despite his otherworldly origins she misses the life she shared with a real man.

The first part of the book, in which the women re-establish their connection, is by some way the weakest. First Alexandra goes on a train trip of the Canadian Rockies by herself, then she joins Jane to explore the Nile. Finally Sukie joins the other two on a package tour to China. Updike is a meticulous observer, but these pages are still too close to travelogue for comfort.

The women find they are compatible enough to want to spend a summer together in their old haunt of Eastwick. They don't actively choose an apartment clumsily carved out of the mansion rented by Darryl Van Horne in the earlier book, but it's the only suitable one available. They are bound together more by memories, both pleasurable and guilty, than any continuing supernatural connection. Witches in Updike's version of them don't ripen in old age. Their powers are an aspect of sexuality, though unleashed by separation, and have undergone a hormonal waning. The cover of the book shows an image of a toad gazing disapprovingly from a dainty teacup. The book's own images of black magic are much homelier and less obvious. Conversation before a sabbat is likely to concern the catering - 'The Munster is delicious. The Gouda seems dry.' Alexandra creates a magic circle with granules of dishwater detergent, which has the advantage (important in rented accommodation, where there's a deposit to be reclaimed) that it can be vacuumed up without trouble after the ceremony.

Updike's prose is barer of flourishes than the earlier volume, and has noticeably fewer art references, as if he was forswearing second-hand seeing. The writing shows no sign of waning powers - it doesn't suggest a late style, or else it always did. If there is a note of farewell, it plausibly belongs to the characters rather than the author: 'Alexandra saw that right here, in front of her, was one answer to death - her genes living on. The tussle of family life, the clumsy accommodations and forgivingness of it, the comedy of membership in a club that has to take you in at the moment of birth.' This would seem sentimental in another context but is sharpened by the knowledge that family life, in the earlier volume, was exactly what the witches, neglectful mothers and (almost) proud of it, despised.

Of the big four of post-war American fiction (the others being Bellow, Mailer and Roth) Updike is the one who, despite his psoriasis, has always seemed most at home in his own skin and in the world. He is also the only gentile, though he exposed that difference imaginatively through the character of Henry Bech. Never mind that his Bech books were among his least successful - it was a significant attempt. In the Rabbit series he explored what it might be like to have a background like his without the creative gift. Again, there are objections to that impressive series of chronicles. It seems rather a cheat to have flooding back into every exquisite sentence the exquisiteness of perception you're supposed to be doing without.

So Updike's imagination is stimulated by difference - except in the case of male homosexuality, which retains stubborn links for him with evil, pretence or futility. The big four were a pretty homophobic bunch on the whole, and the bisexual character on offer here is as deep as any of them managed to go. It's a small sorrow to accept that Updike in this single respect hasn't shed the assumptions of his generation.

Philip Roth's standing is currently higher than Updike's, thanks to an Indian summer of creativity (starting with Sabbath's Theater) so intense that his books should come with complimentary sunblock. Yet Roth sees sexuality from a narrow range of angles. He struggles to show women except as the objects of desire, and it's impossible to imagine him bringing off a book, like this one and its predecessor, with women's own desires at its centre. The sexual adventures in The Widows of Eastwick are almost entirely in the past, but the memories are luminous, and it's an extraordinary achievement to show men, and their little sexualities, as if from outside.

It counts against Updike that he doesn't reproach the world, or rail against it, but seems content to register it. At the fantastically high level at which he undertakes that registration, it is alchemy enough.