Someone is polluting Small Shadow Lake, and it looks like a job for the two young detectives. Their neighbour, Erin Darby, has the scientific skills they need to crack the case. But Erin's a mystery herself. What's she so afraid of? And what's she got against Polly? If Polly wants to solve the mystery of the polluted lake, she may have to figure out what's bugging Erin first.