Sometimes novels come up short. It may happen to you. Before beefing up the story with new characters and subplots, however, make sure you’ve tended to its depth. You might want to follow this simple plan: Seek out the “hot” story moments worthy of further mining (they will look suspiciously like emotional turning points). Apply added word count there.  We readers want to linger in emotionally rich moments. Such turning points are the purpose of the fiction—we've suffered along while extreme pressure is brought to bear on the protagonist, and reveling in her moments of indelible change, both small and large, is our reward. To make that change believable the reader needs access to the inner torment of the point-of-view character. Real change never results from hasty decisions—the protagonist needs to be wrestling with some big issue that will ultimately reveal her true character. In the gothic novel The Thirteenth Tale , here’s how author Diane Setterfield pulls off a lon...