The duel in question is chess: Fisher vs. Spasky. At the height of the cold war this pitches the US against the USSR an brings Iceland to center stage of world attention for a few weeks. The killing of a young boy in a cinema and the security and paranoia surrounding the duel are at the center of the story. Somehow they seem to be linked.
Though there is a connection to his Erlendur series, this is really a standalone. The backstory of the main investigator illuminates another aspect of history: the impact of tuberculosis before a cure became available. Here again Indridason's strength in conveying a strong sense of place is evident.