Katie Cooper is a typical down-to-earth school girl. She never thought about solving crimes until she lost her pet hamster, Fred, in a school fire set by an arsonist. After that, Katie and her friends became committed crime solvers. Katie loves science, and she's good at gathering evidence and drawing conclusions. But detective work is tricky. Not every clue leads to an obvious conclusion or points to a clear suspect. As she follows leads to find the arsonist, she soon discovers that detective work can be dangerous too. In this series of mysteries, Katie Cooper and her friends investigate some serious crimes. In the process, they meet some unusual people and learn a whole lot as they carry out their investigations.