Don't just take my opinion look at the knowledgeable Maxine of Petrona's review here.
Ernst Sigurd Karlsson kills himself with a shot through the mouth in his tidy bedroom. Alongside the phone in the living room is a pad with two words written on it. Martin Beck.
Meanwhile Gunvald Larsson is observing a Stockholm apartment house, while a young policeman gets some coffee to warm him. The house explodes and Larsson heroically rescues most of the people inside.
Why was the house being watched? Was the explosion arson or an accident?
The investigation is an ensemble operation, breaking several of S.S. Van Dine's rules for writing detective stories [listed by Kerrie at Mysteries in Paradise], with the conflicting idiosyncratic personalities of the detectives playing a major part in the story. Systematic police work, stinging social commentary and a lot of humour makes this book a great read.
Martin Beck takes an ancillary role in this story apart from the details of his almost always depressing home life which leads him to lie to his wife and spend the holiday weekend with Kollberg and his wife.
The slightly concussed Gunvald Larsson conducts his own off beat investigation while supposedly off sick. But Martin Beck and the rest of the team, Lennart Kollberg Einar Ronn, Fredrik Melander [when he is not in the toilet] , and 'future Chief of Police' Benny Skacke end up needing the cooperation of Inspector Mansson from Malmo who conveniently finds a very helpful witness in order to solve the interrelated crimes.
A lot of the black humour in the book concerns the team members and their relationships with minor characters such as their boss Hammar, criminal-technologist Hjelm, and the 'Laurel and Hardy' of the Stockholm police Kvant and Kristiansson.
'Except a false alarm, which you failed to report, for Christ's sake. Out of sheer idleness or stupidity. Is that right?'
'Yes ,' mumbled Kristiansson.
'We were exhausted,' said Kvant, with a glimpse of hope.
'Lengthy and demanding duty.'
'Christ, kiss my arse,' said Gunvald Larsson. 'How many arrests had you made during your patrol?'
'None', said Kristiansson.
If you have not read this series yet you are in for a wonderful treat and I can do no more than quote the Birmingham [UK] Post;
'Sjowall /Wahloo are the best writers of police procedural in the world.'