Hypothermia by Arnaldur Indridason

I've always loved Arnaldur Indridason's police procedurals, but Hypothermia is my new favorite.  Icelandic detective Erlendur Sveinsson starts poking around in what appears to him to be an open-and-shut suicide case, after he is given a tape recording of a seance the deceased woman had with a psychic before her death.

Lake Thingvallavatn

Maria's suicide seems to be linked to Lake Thingvallavatn, as she hung herself in her cottage by the lake, and as a child witnessed her father's death by drowning in the same lake. She also had a great curiosity about the afterlife, going so far as to arrange for her dying mother to give her a sign if life after death existed. Chilling in more ways than one, Hypothermia is the perfect book for a hot day.