Little by little, Penny Lowry is making it through the fifth grade—with a bit of help from her friends Maria, Kristian, and Rocco, as well as her lovable dog Cosmo. And there's a lot of change to deal with this year! Penny's newborn twin brother and sister have everyone in her family on their last nerve with their crying. Her friends Maria and Chloe are spending a lot of time together without inviting Penny along, making her worry they might be getting tired of her. And on top of everything, Penny and her friends discover a very old map in her attic that sends them on a wild scavenger hunt all over town in search of treasure!

Can Penny get her worries about her friends and family under control, and lead her group of friends to find the hidden treasure?