In 1871, when students sailing from Iceland to Copenhagen devised a quiz about the text of a famous medieval manuscript to entertain themselves on the journey, they never suspected that their unsolved riddle would become the center of a gruesome murder mystery decades later.

So explains Viktor Arnar Ingolfsson in his new novel, The Flatey Enigma, which is steeped in the mystery surrounding the Icelandic Book of Flatey, a medieval tome that recorded the histories of the Norse kings. Each chapter of Ingolfsson's international best seller ends with a clue (and an answer) from the 40 questions in the so-called Aenigma Flateyensis puzzle. The 40th question—and the key to the riddle—has never been solved.

The Flatey Enigma begins with the death of professor Gaston Lund, a Danish cryptographer who visits the tiny island of Flatey to decipher the Aenigma Flateyensis once and for all. When his body is discovered on a deserted island nearby, no one knows why he failed in his quest.

Soon after, another body is uncovered with a Viking symbol carved into its back. Kjartan, a young lawyer from the district magistrate's office, is assigned to investigate. All connections lead back to the riddle of the Book of Flatey. Had Lund solved the puzzle, only to perish?

As Kjartan unravels the clues, myths, and codes surrounding the Aenigma Flateyensis, fans of Nordic crime writers such as Henning Mankell, Karin Fossum, and Arnaldur Indridason will relish the cleverly plotted layers of this Glass Key–nominated mystery.