When I reviewed William Gibson’s groundbreaking novel, “The Peripheral,” nearly six years ago, I dared to hope for a sequel. And now we have it in “Agency,” a book as engaging, thought-provoking and delightful as its predecessor. While the novelty of Gibson’s core conceit — virtual time travel across parallel universes, not in the flesh but by high-bandwidth communication — is no longer as startling, he still manages to squeeze fresh juice from the novum. Strong co-starring characters unique to this tale interact with returning old favorites. A wistful continuum premieres — in which Hillary Clinton won the presidency in 2016 — offering plenty of opportunity for cultural commentary. And the intricate noir-thriller plotting affords constant entertainment and suspense.

We begin, however, rather sedately and in semi-familiar circumstances, allowing the reader, newbie or veteran, easy access to Gibson’s scenario.

Our heroine is Verity Jane, a young woman living in contemporary San Francisco, whose arcane profession is “app whisperer.” Basically, she tests unreleased software products to reveal hidden flaws and make them secure and reliable. Having recently split from her lover, Stets Howell, a rich entrepreneur, Verity is couch-surfing in the slightly sleazy apartment of a ditsy bachelor buddy, Joe-Eddy, and feeling at loose ends.

Her newest gig is with a firm named Tulpagenics, which presents her with a pair of ­augmented-reality eyeglasses, a special cellphone and a headset, and has her exploring without explicit instructions. Booting up the rig, she is confronted by the avatar of a woman who calls herself Eunice. Eunice proves to be the world’s first fully sentient artificial intelligence, smarter than any human but still somewhat inexperienced and naive. She’s fumbling around for “agency,” that vaunted attribute that endows the individual, silicon or flesh, with willful capacity for action.

Verity and Eunice swiftly become besties. But when Eunice decides that she doesn’t approve of the sketchy future that Tulpagenics has planned for her, she and Verity go on the lam. For Verity, this means hiding out with weird hackers, superspy baristas and other assorted oddballs. But for Eunice, hiding out in the net proves impossible and, a third of the way into the novel, she seems to go extinct.

All this action is interleaved with another narrative. In the year 2136, humanity exists in an uneasy truce with larger intelligences. It’s a post-scarcity, near-singularity situation, although there’s a privileged “klept” caste. Our focus here is Wilf Netherton, a half-willing agent for the scary Detective Inspector Ainsley Lowbeer. Lowbeer has an overriding mission: “She’s altering stubs to produce worlds in which the klept enjoy less power.”

What exactly is a stub? It’s a counterfactual continuum, existing alongside the dominant 2136 world, produced by intervention in the shared past. Not physical intervention from literal time-travelers, but by two-way communications. However, since remote telepresence is a form of communication, folks from 2136 can operate avatars — peripherals — in the stubs.

Thus, Verity finds that one of her outlaw companions is a very competent robot affording Netherton an active presence in the year 2017. Netherton wants Eunice restored as much as Verity does. He also wants to help President Clinton avoid a forecasted nuclear Armageddon originating with a terrorist group in the Middle East.

Does all this sound confusing? I have not even mentioned that Conner, a hardened ex-soldier who figured in “The Peripheral,” is also beaming in from his own distinct stub to help. Or that there are forces in 2136 that want Lowbeer to fail. But you can rest assured that Gibson lays everything out with utmost clarity, and soon the reader is bopping among the various venues as easily as Netherton himself.

Gibson has been dealing with the matter of artificial intelligence ever since his earliest trilogy that began with 1984’s “Neuromancer.” Eunice is an extremely believable, idiosyncratic and highly polished character. So much so that her vanishing takes a little luster off the subsequent action. Her glib confidence and joie de vivre are really missed. But Verity, Netherton and the supporting cast offer plenty of anchoring interest.

Gibson fleshes out the “present-day” venue of 2017 with his patented sharp vision for small and large cultural touchstones. The matter of a Clinton presidency, which received some advance attention from curious readers, is really the least consequential part of the story. And it’s not all peaches and cream.

“They don’t wake each day with renewed gratitude for that particular bullet having been dodged, no,” Lowbeer says of the American people, “but that’s simply human nature.”

Likewise, the world of 2136 is evoked with a deadpan sense of wonder. Netherton’s clothes closet, for example, is really a box full of nanotech assemblers that eat old garments and spit out new ones.

Gibson’s language is as zesty as ever. A robot, for instance, resembles “an eight-legged raccoon in a small antique biohazard suit.” But what is different about this book, and the previous one, is a kind of elder statesman wisdom and optimism. Ironically, the 1980s — retrospectively a less fraught era — generated Gibson’s bleakest scenarios, while the arguably more dire present has seen him moving toward an almost Westlakean mordant lightheartedness.

Regardless of Gibson’s shifting ratios of glee to cynicism, he can always be counted on to show us our contemporary milieu rendered magical by his unique insights, and a future rendered inhabitable by his wild yet disciplined imagination.

Paul Di Filippo’s most recent novel is “The Deadly Kiss-Off.”

AGENCY

By William Gibson

Berkley. 402 pp. $28