When Nancy's parents win an all-expenses-paid vacation, Nancy and JoJo get to sleep over at their neighbor's home, Mrs. DeVine's. But JoJo is a little nervous to sleep at someone else's house—luckily Nancy is an expert on sleepovers and can help prepare her little sister. The big night arrives, and JoJo and Nancy have a blast at Mrs. DeVine's. But when it's time for bed, it turns out Nancy wasn't as prepared as she thought. Good thing there is nothing better than a sister to make you feel better.