The Secrets of the Rock is the third book in the Fribble Mouse Library Mystery Series. While on a clean-up project in the park, Fribble discovers an old rock bearing a brass plaque that is so dirty that he can't read it. When he and his brother and visiting aunt clean up the plaque, they uncover several questions? For whom was the plaque a memorial? Who was the Handcuff King? Why had he made a trip to Cheddarville so many years ago? Why is there a line of music written on the plaque? While finding the answers to these questions, Fribble must use his best library skills. He also must get ready to perform in the big Fall Festival at school.