The Draining Lake: An Inspector Erlendur Novel, Book 4

In the wake of an earthquake, the water level of an Icelandic lake drops suddenly, revealing the skeleton of a man half-buried in its sandy bed. It is clear immediately that it has been there for many years. There is a large hole in the skull. Yet more mysteriously, a heavy communication device is attached to it, possibly some sort of radio transmitter, bearing inscriptions in Russian. The police are called in and Erlendur, Elinborg, and Sigurdur Olii begin their investigation, which gradually leads them back to the time of the Cold War when bright, left-wing students would be sent from Iceland to study in the "heavenly state" of communist East Germany.