The graininess of Inherent Vice makes every frame backwards-looking; the story's nostalgia for 60's dreams mirrored in director P.T. Anderson's nostalgia for 70's filmmaking, and for celluloid itself. But it's also well-suited to the movie's own story and themes. After all, film gets grainy when you're losing light.
Inherent Vice is a movie about left-behind people. They're scuttling around the fraying edges of the counterculture, trying to stay warm by the dying embers of their past, trying not to notice the shadow of money and power as it slowly covers their entire life. Doc Sportello's stoner paranoia is a funny, sad attempt to imagine there's more to the story than the oldest story in the world: greedy assholes taking everything that was free and selling it.
** ALL KINDS OF SPOILERS BELOW **
The plot kicks in from the first scene, when a Doc's lost love Shasta Hepworth shows up with a story about her married boyfriend whose wife is plotting to get him institutionalized so she can take his money. When Doc first sees Shasta, he comments on how she's done herself up all respectable-like, not knowing just how sucked into the system she is; the plan is for a legal kidnapping, the square's version of a heist. The wife isn't mad about his habit of boinking hippie girls, which is just standard bourgeois infidelity. But she's determined to stop his hippie-influenced plan to give up building expensive condos and start building free housing. We can only imagine the delight she takes in making a flower child's honeypot part of her reactionary scheme.
One of the major themes of the movie is a world where all the things once free are being packaged for sale. And the commodification of free love is a big part of that. The scenes of a wanna-be-hip dentist swapping easy sex for good coke may play as a laugh riot, but it's a lot sadder when you consider that these snow bunny deals are being made in an office complex built on top of the vacant lot where Shasta and Doc were once drugless, in love, and free. Making it all the more pointed that Doc is distracted by coke and ass as anyone. As in Pynchon's Mason & Dixon, joy and freedom can only happen in the empty places where money has not yet begun to scheme, and as soon as anyone with power notices, they'll be plowed right under so that someone can sell admission.
And in the movie, as with the historical 60s, ubiquitous sex is the promise that gets suckers through the door. Doc gets a free preview of the pussy eater's special, but the girls are just trying to distract a guy they think is a cop. A closet full of naked-lady ties is a souvenir of all the bodies that real estate money can buy. And when Shasta strips, it's a sure sign that something terrible is happening. Black revolutionaries and Aryan bikers may be the era's rebel motherfuckers, but they end up pawns as surely as the hopeless junkies who will always be good customers "as long as American life was something to be escaped from."
Eventually all the interlocking stories are revealed as a plot of The Golden Fang, a vertically integrated 60s-eating monster, encompassing hard drugs, new age therapy, cosmetic dentistry and pricey real estate– everything you need to build the white man's Los Angeles. The Fang came into the 60s like Dracula drifting in by sea, and sucked the optimism out of the 60s with teeth made of precious metal. But the moneymen washed in on a wave of teenybopper sex, all those drugged-out, hope-addled girls irresistible victims for the dealers, the hustlers, and the frequently name-checked Charlie Manson. Doc's got a good heart, and he wants to save everyone. But he can't stop listening to his dope and his dick, and they keep him wrapped up in obscurantist insights and too-easy pleasures, never seeing the pattern that's right on the surface.