This interesting mystery is situated on Flatey, a tiny island (one by two kilometers) in the cluster of the western islands in Breiðafjörður (NW Iceland). As the name "Flatey" indicates, it is indeed very flat. In 1960, the year in which the story takes place, it has a church, a post office (with one telephone, the only one on the island), a doctor and two shops; the few score of inhabitants are sheep farmers and seal hunters. The island is visited by migratory birds, such as the puffin, which also occupies an important position on the island's menu (together with fermented shark and seal blubber). There is a regular ferry to ports on the Icelandic mainland.
On an uninhabited islet near Flatey seal hunters find a dead man, but no boat or remains of a shipwreck - and nobody is missing from the area. Kjartan, a representative of the district magistrate, is sent to Flatey to investigate the crime. He feels out of his element among the colorful inhabitants such as Grimur, the district officer/seal hunter, the local priest Thormodur Krakur, and the alluring doctor Johanna, who acts as coroner. Kjartan discovers a cryptic note in the dead man’s pocket which he relates to a famous medieval manuscript called the Flatey Book (Flateyjarbók or Codex Flateyensis), which contains a riddle believed to inflict a curse on anyone who attempts to solve its mysteries. At the end of every chapter Viktor Arnar Ingólfsson has incorporated a brief text from that manuscript, each about a violent deed of the Norse kings, and containing one of 40 riddles. Although the original manuscript is kept in Copenhagen (since 1971 in Reikjavik), the small library on Flatey (built in 1864 and the oldest library in Iceland) houses a copy.
The dead man then is identified as Gaston Lund, a noted Danish scholar of Icelandic antiquities known to be obsessed with the Flatey enigma, and now the investigation expands: an investigator from the Reykjavik police and a reporter launch their parallel research. This all leads to an unexpected and very original conclusion.
The novel is fascinating for the realistic descriptions of life on Flatey: the islander's diet, their small cottages, dress, their ethics and religious beliefs, and the fishing industry aimed at seal pups.