Journalist Jerry Markham, a former resident of Shetland Island in Scotland, goes back for a visit and ends up dead. His body is found by Procurator Fiscal (prosecutor) Rhona Laing, in a boat she regularly uses.
Detetive Inspector Willow Reeves is brought in to investigate the crime. She works with two local detectives: Sandy Wilson - an insecure lad who lacks confidence in his abilities, and Jimmy Perez - who is still in deep mourning after the death of his girlfriend, Fran. Willow immediately pegs Rhona Laing as "knowing something" but the local police - loyal to Shetland Islanders - resist the idea.
Investigations reveal that Jerry Markham may have been looking into an island group promotiing tidal energy. 'Green initiatives' are a controversial issue on the island, with some people promoting the idea and others agitating against it. The police come to suspect shenanigans in this proposed business venture. The detectives also discover that Markham is generally considered a spoiled, self-centered fellow who - several years before - had run out on his pregnant girlfriend, breaking her heart and angering her family. Moreover, another body soon turns up, complicating the investigation and widening the list of suspects.
The story's setting is well described, and the reader gets (what seems to be) an authentic glimpse of the terrain and culture of the Scottish islands. The characters - including the detectives and a wide array of suspects - are well-rounded and interesting. In addition to his professional duties we get to know a bit about Jimmy Perez's private life, in which he's raising Fran's young daughter - a sweet, precocious child.
The police investigation proceeds in a logical fashion leading to a finale that's believable but too long and drawn out. All in all an enjoyable mystery.