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?