I don’t know that the Martin Beck series can possibly be better than The Locked Room. It hits every critical talking point the writing staff have tried to address in previous tales and it becomes something else entirely. It’s almost as if this book is writing through the reader rather than to them.
Some series don’t need to be read in sequential order. They may be even better if you don’t do that. I started the Lew Archer series out of order by accident and it’s my favorite detective series of all time. But this absolutely has to be read from Roseanna on because the payoffs are enormous the further you get into the series.
In The Locked Room, Sjöwall and Wahlöö try something I haven’t seen them do yet: write extensively from the perspective of the criminals. You don’t know if these particular criminals did the dirty deed or not but they’re tied into that world somehow and you get a peak at it. And what you find on both sides of the law is that these are not superheroes or masterminds but fatally flawed individuals who do things for their own motives in a country that the writers see as unjust (though I had to cry when the detectives talked about how awful it is to throw someone in jail for life because yes it is). The two mysteries develop over time (this is the longest book in the series so far) and you continue to follow the thread until they reach their rather entertaining and satisfying conclusion.
I cannot give this series enough Hosannas. I read the first book four years ago and was so unimpressed, I knew I would never go back to the series. Someone persuaded me to try book two and it’s one of the best decisions I’ve ever made. I’m always grateful to that person for doing so because I can’t imagine missing out on the excellence of these stories.