I guess it belongs under
the mystery genre. He's a good writer often compared to Eco and $#@!ens for his style of writing. An easy read while still entertaining and interesting with a big gallery of characters that are hold together with a good storyline. Though fiction he often has a very credible description of the conditions in Spain up to the civil war.
I can highly recommend his first two novels if you are looking for some 'riding the train, sitting in the summer sun or taking a break from Kierkegaard'-literature.