Stephanie has had it with her baby brother and sister. All they do is sleep, cry, and eat—but for some reason everyone thinks they’re adorable. Kate knows exactly how she feels, since she has to put up with her own little sister, Melissa the Monster. But then the Sleepover Friends notice something strange is going on. Stephanie starts spending a lot of time with Melissa—styling her hair, taking her shopping for clothes, teaching her how to dance. And Kate wants to know why Stephanie is suddenly trying to be the perfect big sister—to her little sister!