The Flatey Enigma

In the spring of 1960 three men accidentally discover a decaying body on a deserted island, later identified as the body of a Danish codicologist who had been missing for several months. An investigation ensues and the case is mysteriously linked to the contents of a medieval manuscript known as the Book of Flatey. Before long another body is found in Flatey, but this time an eagle has been carved into the victim's back in blood, in the ancient Viking tradition.