Why would suicide need a witness?

On the east coast of Ireland, Victor Delahaye, one of the country's most prominent citizens, takes his business partner's son out sailing. But once at sea, Davy Clancy is horrified to witness Delahaye take out a gun and shoot himself dead.

This strange event captures the attention of Detective Inspector Hackett and his friend Pathologist Doctor Quirke. The Delahayes and Clancys have been rivals for generations and the suicide lays bare the perplexing characters at the heart of the mystery, from Mona, Delahaye's toxic young widow, to Jonas and James, his strange, enigmatic twin sons; and Jack Clancy, his down-trodden, womanizing partner. And when a second death occurs, one even more shocking than the first, Quirke begins to realise that terrible secrets lie buried within these entangled families; and that in this world of jealousy, ruthless ambition and pride - nothing is quite as it seems . . .