Before Stieg Larsson or Henning Mankell — and in my opinion better than either — Sweden had the husband-and-wife team of Maj Sjöwall and Per Wahlöö. Between 1965 and 1975 they wrote ten murder mysteries featuring Stockholm policeman Martin Beck. These were planned as a series, The Story of a Crime, but are independent novels.
Police procedurals, these novels have a narrative driven not by body piled on body with implausibly escalating violence or outré plot elements but by the accumulation of evidence, sometimes by luck and sometimes the result of hard work. The plots are quite varied. The first novel, Roseanna, involves an American tourist found dead in a canal and has Beck liaising with an American policeman. The second, The Man Who Went up in Smoke, takes Beck to communist Budapest. And there are some more dramatic crimes — a serial murderer of children, the gunning down of an entire bus full of people, and in the last book international terrorism. The sub-plots show an equally broad range, highlighting different aspects of Swedish society.
Martin Beck may have the lead role, but he is more like a first violinist than a conductor, with the story often following his colleagues. The closest to an "off-sider" he has is Lennart Kollberg, who is sardonic, fond of food, and not really made to be a policeman. Fredrik Melander has an extraordinary memory and uses it to find unexpected connections. Gunvald Larsson is an impetuous man of action, a dapper-dressing refugee from a bourgeois family. Newcomer Benny Skacke is ambitious and aspiring, but also hard working and willing to learn. And there are others.
Some of these figures are not so attractive at first, but improve as the series progresses and we (and their colleagues) get to know them. Their interactions with one another and their personal lives provide some story material but rarely take over — there's no artificial attempt to connect the investigators' personal lives with the crimes in every story.
Some comic relief is provided by the clown-like patrol team of Kvant and Kristiansson. More seriously, Beck and his colleagues have to deal with a bevy of self-seeking managers and politicians. Sjöwall and Wahlöö were both Marxists, but while the political elements get stronger as the series progresses they are never overpowering. Also, the chief concern here is revealing the dark underside of Swedish society and the corruptions of the Swedish welfare state and justice system, much of which will appeal as much to libertarian- as to left-leaning readers.
One aspect of this is that the criminals always remain human, and in a few cases we — and Beck — end up sympathising with them more than with their victims. Sjöwall and Wahlöö work with a nuanced palette, not just primary colours.
They have just been reissued by Fourth Estate, but I read the Martin Beck novels in the Harper "PS" series, which includes afterwords with short essays, interviews and so forth, often by notable writers. Some of this material repeats across the ten books, but it is informative, giving an idea how important Sjöwall and Wahlöö were in the development of both the police procedural and the broader genre, looking at other husband-and-wife writing teams, and so forth.
Some of the novels are better than others, but they are quite consistent and the recommended reading order is chronological: start with Roseanna and see how you get on.