Bonnie Montgomery is finally getting a vacation from cracking cases as her alter ego, Montgomery Bonbon. But something terribly fishy happens the moment she and Grampa Banks arrive on Odde Island—and it’s not just the smell of the harbor. There’s been a mysterious death at the lighthouse, and what everyone assumed was an accident is setting Bonbon’s mustache all aquiver: something is Highly Suspicious. When a second death takes place, Bonnie is sure the two are connected. But can she solve this case alone, or will she need double the detectives to solve double the murders?