At the beginning of John Updike’s novel “The Witches of Eastwick,” Alexandra Spoffard stands on a beach in Rhode Island and conjures a thunderstorm out of a clear, blue afternoon; she wants the beach for herself and her dog, and she resents the intrusion of carefree, careless young people. The spell and the description of the gathering storm occupy only two paragraphs, but the effect is cosmic and exhilarating, a tour de force of rich Updikean evocation. Such conjuring is emblematic of Updike’s mode of literary creation, his spellbinding inventiveness, his brilliant, provocative powers of physical and psychological simulation.

Published in 1984, “The Witches of Eastwick” is set in the late 1960s, that era of unbuttoned sexual freedom and feminist liberation, of tuning in and turning on. The divorced trio of witches — Alexandra, the sculptor; Jane Smart, the cellist; Sukie Rougemont, a newspaper gossip columnist — is like a hot spot, an exposed nerve, in their small town, where their exclusivity and sexual high-jinks (particularly with married men) cause rumors and suspicion. All three fall for Darryl Van Horne, a wealthy newcomer who buys the old Lenox mansion to use as a base for his dubious scientific experiments — and his cocktail- and drug-fueled orgies; he finds the witches willing participants, together and separately. Inevitably, matters spin out of control, the witches murder a young woman, Jenny Gabriel, who steals Van Horne’s attention away from them and their coven dissolves in confusion and recrimination.

“The Witches of Eastwick” seems an unlikely candidate for a sequel, or perhaps our perception of the book has been warped by the ludicrous movie, much altered from the novel, released in 1987. Rereading the book brings it back into focus as one of Updike’s noble and weirdly irresistible experiments — better than “S” or “A Month of Sundays,” not as good as “Brazil” or “Gertrude and Claudius” — and reminds us that, after all, Alexandra, Sukie and Jane got away with murder before they left town. A sequel may have been necessary to bring things aright.

More than 30 years have passed when “The Widows of Eastwick” opens. The witches, who had remarried after leaving Eastwick, are now widows, seeking to assuage their grief and loneliness through travel. Alexandra tours the Canadian Rockies, then she and Jane go to Egypt, and then the trio visits China. These perambulations occupy the first 100 pages of the novel and prove to be an awkward way to launch a narrative. While this section is filled, naturally, with Updike’s vividly presented insights into social and cultural differences, there are patches of curiously flaccid writing — “China delighted the three women” — and a general air of hanging fire until the action really begins.

The widows decide to spend a summer in Eastwick, propelled by curiosity and guilt over their murder of Jenny Gabriel, but revisiting the scene of the crime after three decades proves disconcerting. The witches discover that making amends is not easy. Eastwick has lost its “messy charm,” becoming a typical quaint, gentrified bedroom community filled with gourmet shops and SUVs. Few people survive who remember Alexandra and Sukie and Jane, and those who do remember hold grudges. Now in their 70s, mainly castaways from the sensual life of the body they once pursued so avidly, the women feel mortality stealing upon them. Seeing boisterous teenagers outside the Superette, Alexandra thinks: “Little do they know what lies ahead of them. Sex, entrapment, weariness, death.”

Bathed in summer’s golden light that fades to autumnal dimness, “The Widows of Eastwick” conveys an elegiac tone; Updike does not spare his heroines much in the array of aches and pains and the daily debilitations of the elderly. He treats the women far more tenderly than he did in this novel’s predecessor, a fact that robs “The Widows of Eastwick” of prickly energy and bite. Still, it’s amusing and sad to see the aged women, naked and vulnerable, attempting to cast a spell with a plastic broom, a “tinfoil” chalice and a jug of Carlo Rosso Chianti. They are trying to counteract a hex placed upon them by Jenny Gabriel’s vengeful brother Chris, but the dire result is not what they expect.

There are many levels on which any work of fiction by John Updike is not only enjoyable but frankly intriguing and often compelling. When the Museum of Sentences opens, Updike will have a whole gallery. Yet while “The Widows of Eastwick” employs the author’s usual tropes with his habitual blandishments — emphasis on the body and its functions, especially sex; a preoccupation with nature and seasons and weather; a brave and almost reckless delving into the psyches of women (or his women) — the novel does not form a coherent narrative. Not that one doesn’t sympathize with the aging witches; one simply wishes that the sequel they inhabit exhibited more magic, another of those thunderstorms summoned out of the blue.