Trollope's brisk novel features siblings David and Nathalie, born to different women and adopted as children by an infertile British couple. As adults, they track down their biological parents -- with predictably disruptive effects. Trollope dutifully explores the trendy subject from every possible angle: We get the icy hauteur of David's birth mother, who feels no bond with the child she abandoned decades ago, and we get the petulant anger of her ''legitimate'' son, who resents her secret past. Nathalie's husband, feeling excluded from her quest, begins an affair, while David's marriage grows stronger. In fact, we're offered a few too many perspectives. At times, this cool, smart book reads more like a sociological survey than a messy, particular, and personal work of fiction.