A leftist tendency and a dramatically effective narrative distinguished Wahlöö's early novels about power and the right, for example "A Necessary Action" from 1962, which depicts Franco's Spain, and his "Dictatorship" series. From the mid-1960s, he wrote together with life companion Maj Sjöwall a series of detective novels with criminal investigator Martin Beck as protagonist. Several of them have been filmed, and a Swedish TV film series began running in 1997, with Peter Haber as Martin Beck. The series was bought by the BBC in 2015, and shown in the United Kingdom with English subtitles.