This is the story of Ella Addison, an extraordinary 12 year old girl who swims with sharks. It is a family tradition. But something strange is happening around her Shark Rock playground. Black tip sharks are multiplying and tiger sharks are disappearing. Curious by nature, Ella starts a school project aimed at solving this mystery. Normally, black tips migrate to Shark Rock for the salmon run, and then move on. But in recent years, they are staying put. This means tiger sharks are being forced out. So where do the black tips come from? Why are there only females there? These happen to be the same questions that intrigue Jessica Escobar, a feisty Columbian marine biologist doing her doctoral thesis on black tips. Ella and Jessica make a formidable team. While Jessica compiles and analysis the genetic information, Ella compiles a visual diary of her dives on Shark Rock to present to her school. But can they solve the riddle of Shark Rock? Or is the black tip invasion unstoppable?