“At least there is at hand a testament—this first novel ‘V’—which suggests that no matter what his circumstances, or where he’s doing it, there is at work a young writer of staggering promise.”

So began the literary career of Thomas Pynchon, whose latest novel, “Inherent Vice,” we gather here today to celebrate. Since George A. Plimpton ’50 wrote the above praise some 46 years ago, Pynchon has indeed succeeded in turning staggering promise into staggering achievement. His third novel, 1973’s “Gravity’s Rainbow,” is one of those works—like Joyce’s “Ulysses” or Wallace’s “Infinite Jest”—that literary junkies force themselves to read and pray that they’ll one day understand. He has received a National Book Award (for that novel), a MacArthur “genius grant,” and is consistently on the rumored short list for the Nobel Prize in Literature.

All of this perhaps explains why the critical response to “Inherent Vice,” released earlier this summer, has been long on career retrospection and short on evaluation. So let me say it now: “Inherent Vice” is not a very good novel. It’s not engaging. It’s not inventive. It’s not intricate, and it’s not precise. What it is, though, is an opportunity to examine the stately decline of one of literature’s most enigmatic and gigantic figures.

“Inherent Vice” is a typically Pynchonian take on the detective genre, starring Larry “Doc” Sportello as a sandal-wearing, beach-dwelling, pot-smoking Private Eye. The paranoiac narrative—situated historically around the 1970 Manson Family murder trial and geographically around the fictional Gordita Beach on the California coast—begins when an old flame named Shasta Fay approaches Doc with a vaguely defined mission: to protect her current boyfriend, real-estate heavyweight Mickey Wolfmann, from the shadowy forces trying to put him on ice.

And then she disappears. In the process of trying to find Shasta—and Mickey, who disappears simultaneously, but separately—Doc winds up entangled with an undead saxophonist, a contract killer, several drug dealers, and a dentist, all somehow connected to a sinister outfit called the “Golden Fang.”

For a primer to help you decode what seems convoluted in “Inherent Vice,” look to Pynchon’s second novel, “The Crying of Lot 49,” an altogether more effective version of the same basic literary ideas. That novel is also a paranoia-infused narrative set in California, in which an (amateur) private investigator (“Oedipa Maas”) is on the trail of another sinister outfit (“W.A.S.T.E”), a trail that leads her to just as many interesting characters and down trippy narrative side streets, with names even fruitier than the characters in “Inherent Vice” (“Pierce Inverarity,” “Randy Driblette,” “Genghis Cohen”). It’s also half the number of pages.

In ways both formal and thematic, “Inherent Vice” is a Pynchon nostalgia trip, one more journey to the author’s literary roots. It’s interesting to watch a man of such genius walk back over familiar ground, this time with the beneficial wisdom but the consequential loss of stamina that come when a great writer ages. In his review for the “New York Review of Books,” Michael Wood classed the book as “a shaggy detective story parodied by Thomas Pynchon, or perhaps like a moderately baggy Thomas Pynchon novel parodied by a devotee of the detective story.”

“Inherent Vice” lacks the energy and inspiration that propelled “The Crying of Lot 49” to become a twentieth century classic. It might have turned a cheap noir pastiche in lesser hands, the work of a writer resting on his laurels or trying to pick up a check. But given the extent to which the detective genre informs novels like “V.,” “The Crying of Lot 49,” and “Gravity’s Rainbow,” and the somehow hypnotic quality of even the book’s mangiest sections, it’s clear that Pynchon retains a deep affection for the genre even now. Similarly, his novels have always dabbled heavily in references to the pulp novel’s cultural siblings—rock music and monster movies—so, despite the seeming retreat into genre fiction, he maintains a continuity of style, if his substantive fingerprints are still conspicuously absent.

Unfortunately, the rigid pacing and logical arc of the conventional detective story don’t quite jive with Pynchon’s classic (one might say, inherent) psychedelia. The novel really does feel shaggy and baggy, because the normally lean detective genre has had to loosen up to accommodate Pynchon’s wild narrative loops and quixotic scenic fancies. When the dentist’s secretary pauses a plot-advancing conversation to ask Doc’s friend—“Excuse me, . . . is that a slice of pizza on your hat?” —the irksomeness of the interruption overshadows the humor of his response (“Oh wow, thanks man, I’ve been lookin [sic] all over for that…”)

Some of the author’s old tricks still dazzle though, as when Doc buys “Wyatt Earp’s personal mustache cup” from a man in Las Vegas whose name turns out to be a “byword of fraudulent Earpiana.” But it turns out to be authentic against all the odds—excessive faith is, after all, the flipside of paranoia.

Perhaps with all his Nazis, conspiracies, and marijuana, Pynchon is actually a creature of excessive faith. Following the clues in a 40-plus-year literary career leads one to the idea that Pynchon will keep on producing, slowly and steadily, until he just keels over. Although he fulfilled the promise Plimpton saw many years and more pages ago, “Inherent Vice” demonstrates that Pynchon is always willing to go back to the well, with the faith that there will still be something there.

—Staff writer Jillian J. Goodman can be reached at jjgoodm@fas.harvard.edu.