When Grace and Ron find an old tin buried in the sand at Sun Valley Lake, the Dragonflier Kids stumble on a history mystery. With the help of their new friend, Jenna, the kids learn about Clemmie and Lottie who met in the early 1900s in Sun Valley.  They discover photographs, letters and diaries that help them answer their questions about this unlikely friendship.  When Grace is anxious about her upcoming gymnastics meet, she discovers that everyone worries sometimes and her friends and Odie help her to learn ways to calm her worries.