Best friends since college Leigh, Adriana, and Emmy are all immersed in busy, fabulous New York City lives that nonetheless afford them plenty of time to sit around watching Grey's Anatomy and moan to each other about their problems, chief among them the horrifying fact that they are all on the cusp of 30. Leigh, a hard-driving editor at a publishing house, fears she doesn't actually love her sports-commentator boyfriend. Her thoughts on his kissing technique: ''His tongue probed too voraciously; his lips always seemed either rigid or fleshy.'' Nonetheless, because he meets every single criterion on her ''checklist,'' she accepts his marriage proposal. Mistake? Hmm. Adriana too is angling for a man before the incipient crow's-feet go on a rampage. A flamboyant Brazilian beauty, she spends her days gossiping with her gay hairdresser and her nights seducing any boy who catches her eye, making sure to dash away as soon as the sex is over in order to preserve her ''mystery.'' Also on the loose is prim Emmy, who recently lost her boyfriend to a nubile bimbo whose favorite book, as listed on her MySpace page, is The South Beach Diet.

The plot revolves unsteadily around an absurd pact between Adriana and Emmy: Adriana vows to find a steady squeeze and remain monogamous for a year, while Emmy will take a ''Tour de Whore,'' sleeping with as many men as she can while traveling the world. It's a gimmicky setup, but it gives Weisberger a structure — one that she promptly, foolishly ignores. The story lurches off in random directions: Emmy's sister becomes pregnant, the gals vacation in Curaçao, Leigh goes home for a tense dinner with her folks in Greenwich. The novel would be unreadable but for the briskly outrageous Adriana. Her sublime and outspoken confidence in her native Brazilian smarts about men borders on self-parody. Meticulous about her sexual rules, her waxing habits, and her weight, this witty young woman may be unapologetically shallow, but she has zero tolerance for what this book is full of: flab.