Anna Pigeon is a park ranger and law enforcement officer in the US National Park Service and this tale is set in Lake Superior's National Park. This is early in the series and later Anna will return to an island on the lake in 'Wolf Study', in winter. This book however involves diving, boating and tourists galore, which confuses the issue when a newly dead body is discovered in a sunken ship. Only a scuba diver could have placed the body in this location and Anna has to investigate despite never knowing if she can trust a diving 'buddy' who may be the killer. Long sunken bottles of vintage wine provide a possible source of wealth - provided they have survived intact. And there is definitely something creepy about the brother and sister diving instructors. Anna is a widow who occasionally turns to drink to dull her grief, loves animals and nature, and belongs in the wilderness. The author has herself worked in the Park Service and is realistic about pay, conditions, prospects - both work and social - and red tape in this career.