Scott Westerfeld's So Yesterday is a nifty little piece of subversion: a sort of junior culture jammer's handbook with a hefty dose of Malcolm Gladwell's The Tipping Point, somewhat thinly disguised as a young-adult mystery. Seventeen-year-old Hunter Braque is a professional cool hunter — a consultant paid by an ad agency to report on rapidly evolving fashion trends. His boss Mandy vanishes after setting up a secretive meeting, and he searches for her with the aid of his enigmatic new friend Jen James. The mystery probably won't even compel teen audiences — Hunter's a little dense about picking up on clues, the story arc is obviously foreshadowed, and the book's biggest real puzzle is why Jen is attracted to Hunter.

But that's okay, because So Yesterday's pleasures aren't dependent on the mystery plot.

Westerfeld drops gleeful, entertaining, unlikely sounding (but easily verifiable) science on nearly every page, bouncing from the history of the color purple to the seizures inspired by Pokemon episode 38 ("Computer Warrior Polygon") in 1997. It all goes down easily because Hunter's narrative voice is consistent and credible: he's a crypto-geeky overachieving wise-ass student of pop culture. He's so obviously enthused about all the weird stuff he knows that he's bursting with the desire to share — it never feels forced, so the novel never seems scare-quotes-educational. He's also so giddily eclectic that virtually any reader is likely to learn something new.

Hunter isn't So Yesterday's only fresh, interesting voice either — he's well matched by Jen James, and their awkward/sweet courtship dance provides the plot impetus that Mandy's disappearance doesn't. I especially liked Jen's take on NYC geography:

"This is the Crème Brulée district."

"Pardon me?"

My sister identifies neighborhoods by the dominant dessert served there," Jen said. "We're west of green tea ice cream and south of tiramisu."

But it's the meta-textual level of So Yesterday that got me really excited. When Hunter meets Jen, he immediately notices her footwear:

The shoes were off-brand black runners, the logo marking erased with a black laundry pen.

Definitely an Innovator, I thought. They tend to specialize, looking like Logo Exiles until you get close.

It's no coincidence that "Logo Exile" is capitalized. The mark of respect accorded to brand names is instead given to a conscious decision not to wear advertising. When Jen in turn remarks on Hunter's snazzy high-tech cell phone, he pretends surprise:

"My phone?" The list of features was on my tongue, but this was the part of the job I didn't like (which is why you will read no product placement in these pages, if I can possibly help it).

He caves scarcely a chapter later:

Lexa Legault had been tapping at her wireless notebook and said, "I got nothing. Zero relevant hits on . . ." she named a certain Web search tool whose name means a very large number. (Oh, forget it. I'm not going to get very far telling this story if I can't say "Google.")

But Hunter goes to great lengths to avoid referring directly to "Apple," "Nike," or "Starbucks." It's so obvious (and it feels so artificial) that it sends a powerful message about the pervasiveness of product placement. And although it adopts some of the language of Gladwell's The Tipping Point, its fundamental subtext is very different. It's not about how you can spread messages more effectively; it's about being aware of the tactics used to deliver messages to you — including the tactics that So Yesterday uses to deliver its message.

Peeps, Westerfeld's newest novel, is even better. Like So Yesterday, it operates on multiple levels. Peeps is more upfront about its objectives. The odd-numbered chapters are fiction and move the plot forward. The even-numbered chapters share the narrative voice of Cal, but they present factual information about a wide assortment of parasites. They're brief, not very technical, colorful and frequently grotesque, and thought-provoking. Westerfeld provides a bibliography for the skeptical and the curious.

In the odd chapters, Peeps presents one of the cleverest and most original angles on non-supernatural vampires that I've ever encountered: vampirism is an infection by a rare and extremely specialized parasite. Other writers have explored vampirism-as-disease (and porphyria provides some real-world inspiration), but Westerfeld does a remarkably good job of suggesting how evolutionary forces could produce his parasite. (He even explains vampires' legendary distaste for mirrors and crosses, something I can't remember any other vampirism-as-a-disease story tackling successfully.) Meanwhile, the factual chapters make a surprisingly compelling case that Westerfeld's fictional parasite is not qualitatively weirder than parasites that actually exist. The meta-message is also clear: this isn't a book that promotes "Intelligent Design"; it's a book that sails on the Beagle with Darwin.

Peeps has a smidgen of So Yesterday's second-biggest weakness: Cal is pretty bright, except when the plot structure requires that he fail to piece something together — then he sprouts a convenient mental blind spot. But Peeps delivers genuine suspenseful creepy action aplenty. It's very unlike Buffy the Vampire Slayer in important respects: there's no supernatural mumbo-jumbo, and it's not primarily about inverting traditional male-female roles in action stories (though there are strong female characters). But like Buffy, it moves quickly and mixes funny/scary/sexy into an intoxicating blend; I could see Buffy fans liking Peeps a lot, and I think it could make an excellent movie if it could be filmed without dumbing it down.

Peeps has a satisfying resolution, but it's definitely open-ended. I closed the book eager for a sequel, and was delighted to learn recently from Westerfeld's website that he's already working on it.