A new book from Thomas Pynchon is always a big deal. Fans may not camp out in front of bookstores Harry Potter–style, but bookish people celebrate new novels from the reclusive author in an excited, covetous mood that most people reserve for expensive tickets to rock concerts. On July 21, Robert Sindelar, the managing partner of Third Place Books, Twittered: "Got my hands on the new Pynchon yesterday. I'm reading it covered in a brown paper bag so no one tries to steal it from me."

The release of Inherent Vice (it goes on sale on Tuesday, August 4) is an especially big deal. It diverges from Pynchon's regular pattern: Whereas he's released a thick novel every 10 years or so for almost a half-century, Vice comes only three years after Against the Day—and for the first time in 43 years, Thomas Pynchon has written a slim, breezy book.

It doesn't resemble the physical shape of his other novels, which are traditionally ponderous and sprawling and messy. (Until now, the usual question that greeted new Pynchon books has been: Is it a well-defined, brilliant mess like Gravity's Rainbow or an oddly shaped, indulgent mess like Mason & Dixon?) When placed on the shelf, Vice (369 pages) looks nothing like Against the Day (1,085 pages) and V. (560 pages), and it doesn't read like them, either. While many of his books toy with genre—Gravity's Rainbow gleefully molests war-fiction tropes; Against the Day's Chums of Chance are a puckish homage to the boys' adventure stories of Pynchon's youth—Vice is unabashedly a mystery.

Pynchon has clearly read a lot of mystery novels of questionable provenance—everything about Vice, from its ugly, neon-lettered cover to its down-on-his-luck private investigator Doc Sportello, positively reeks with the pungent odor of the dime-store gumshoe thriller. It begins, as all good mysteries do, with a woman from Doc's past ("Tonight she was all in flatland gear, hair a lot shorter than he remembered, looking just like she swore she'd never look") wandering back into his life with a problem in tow. Vice is set in the late '60s and Doc is an unrepentant, dope-smoking dropout, the backwash of the Woodstock generation. He smokes his joints down to nothingness—you could condense Vice into a 50-page treatise on the handling of roaches—and his memory is a clouded, cottony haze.

Doc "automotively grop[es]" around Los Angeles in his nondescript car (everyone else in the novel owns cooler rides, and Vice lovingly describes many of them: a ragtop Cadillac, a T-Bird, a "454 Big Block Chev"), not so much actively trying to solve the mystery as asking his friends what they think he should do about it. Along the way, he gets distracted by an enormous conspiracy controlled by an organization—or a person, or maybe a boat, or maybe all three—called the Golden Fang. It's a name right out of a Sax Rohmer Fu Manchu thriller, and the building that may or may not serve as the organization's headquarters is pure pulp: a six-story ornate golden fang, supposedly populated with dentists' offices.

Pynchon hasn't been this accessible since The Crying of Lot 49. He's obviously having fun, and it's hard not to picture him giggling at his typewriter as he plowed through page after page of Vice. The narrative is festooned with digressions and details that mirror Doc's addle-brained thought processes and also function as a kind of secondary language, making Vice a tone poem constructed from American cultural detritus. We hear about a popular myth among beach bums that Jesus was a surfer on the Sea of Galilee (one surfer comes into possession of a piece of the One True Board). A few pages later, we listen in on an argument about "the two different 'Wipeout' singles, and which label, Dot or Decca, featured the laugh [at the beginning of the song] and which didn't." The book throbs with popular culture. References to movies are followed by the film's date of release as in a critical essay—"that supernatural DeSoto in which James Stewart, gone round the bend of love, tails Kim Novak in Vertigo (1958)"—and Pynchon supplies enough fictional song lyrics (by artists like Droolin' Floyd Womack) to transform the book into a musical.

Like any paranoid ex-hippie, Doc maintains a healthy belief in conspiracies and "secret" information—the kind you can find on the shelves of any new-age bookshop. As he searches for someone named Wolfmann (and has to deal with a cop named Bigfoot), he keeps uncovering information about Atlantis and its lesser-known Pacific Ocean sister city, Lemuria. As Doc wrestles with these layers of conspiracy, many of which don't exist until his pot-addled brain creates them, he reveals the book's central conflict: Vice is about the way our practical, hairy ape brains can scuttle their own ambitions by idly creating strange fictions that then become too real to ignore. It's a battle that has raged through most of Pynchon's work in one way or another.

Beneath it all, surfacing sporadically like a cheap serial villain, is the nascent internet, which in the late '60s was called the ARPAnet. One of Doc's friends introduces him to the prototypical World Wide Web, and he increasingly relies on it for information. He wonders why "they"—the men he's positive rule the world from a smoke-filled room—don't make it illegal, the way "they" criminalized acid. Pynchon, doing some of the nimblest, most whimsical work of his career, doesn't provide the answer to that mystery, or many of the mysteries in Vice for that matter, but he shares his infectious excitement about living in a world full of useless, beautiful ideas. For Pynchon, it's not the truth but the search for the truth that matters. recommended