Now how did actress Parker Posey wind up here, smiling through a sentimental sitcom? Brisk, brittle, stylish, she could have been stealing scenes on Cashmere Mafia or Lipstick Jungle. Instead she's playing Sarah Tompkins, a single Manhattan career woman who, learning she can't conceive, decides to use her sister as a surrogate. The sister, named Coco (Lauren Ambrose), is a sour-looking underachiever who doesn't belong (and hasn't been present) in book editor Sarah's world. But the sisters have a strong bond—the show's title refers to a fictional character Sarah based on Coco's childhood imaginary friend—and a deal is struck. It's a cute, warm concept, but it's also pretty hard to imagine Posey and Ambrose (Six Feet Under) sharing appletinis, let alone DNA.