SO YESTERDAY

Aptly-named Hunter spots street trends for "a certain shoe company named after a certain Greek god." When he meets Jen, he notices her unique shoelaces, and realizes she is an Innovator, a person who invents trends (he's a Trendsetter, someone who is "cool, so when they pick up an innovation, it becomes cool"). Mandy, Hunter's boss, invites Hunter and Jen to do some "original thinking," but when the two arrive at the location, they find only her cell phone—and "the coolest shoes we'd ever seen." The pair begins their search for Mandy and the people behind the shoes, before the "bad guys" get Hunter. They depend on other cool hunters, from tech-savvy Lexa to high-society Hillary, to help decipher the clues, and they take risks themselves (going undercover to a posh party, breaking into buildings). There's fun to be had (at the party, rich guests get shampoo samples that turn out to be purple dye), and while readers may lose track of pieces of the plot (or not quite believe the roller skating leader of the underground), they will get swept up in the mystery. Hunter weaves in compelling stories, such as how purple became associated with royalty, and draws a parallel between the spreading of trends and a flu epidemic. (Though the hero refuses to name brands, readers will quickly figure out product names based on his clues.) Ultimately, Westerfeld's (Midnighters ) entertaining adventure doubles as a smart critique on marketing and our consumer culture. Ages 12-up. (Sept.)