It is 1979, a few years after Reykjavík Nights closed, and Erlendur is now a detective, already divorced, and is working for the shadowy Marion Briem. A body of a man has been found in the blue lagoon, which has not yet become the tourist spot it is today. Apparently the victim fell from a great height, and at first the police investigate the possibility that he has been thrown out of an airplane. In parallel, Erlendur is asked to investigate the cold case of a young girl who vanished into thin air on her way to school forty years earlier.