I had been a bit disappointed by the previous season of Prime Suspect as I wasn't that keen on the new format they adopted - three long (yet shorter) episodes, a different story each. I had been used to those mammoth two-parters that were lasting for ever but allowed for a really immersive experience in the story of each season and those of season 4 felt underdeveloped in comparison. (The third one was better but that was because they returned to the original story of season 1 and expanded it in interesting ways).
So I was glad to see here a return to the previous format and a return to form. This is Prime Suspect at its best, very similar to the first season in a sense, as we know who the culprit is from early on and it's only a matter of trying to find evidence to convict them. Again in typical PS fashion, the unravelling of the main plot is acompanied by an engagement with issues of institutional discrimination and prejudice (not only gender here but also race - this would have been filmed under the shadow of the Stephen Lawrence murder - and the experience of being an outsider transferred from London).
The writing does get clumsy at times, but no-one is perfect: so how is it that a witness to a crime runs hiding yet they floorboard their flat opposite the scene of the crime? Could anyone make it more obvious to everyone else that they've left? Or the cliffhanger of part 1 *SEMI-SPOILER HERE* why shoot the person shot rather than turn around and shoot the person right next to you? *END OF SEMI-SPOILER*
Mirren is excellent here as always, and there's a couple of great actors who unfortunately seem to have had a rather brief career, like Julia Lane as DI Devanney and John Brobbey as Henry. David O'Hara is very good too as DS Rankine but the show is literally stolen by Steven Mackintosh who is simply superb as The Street, the character and actor whose presence really defines the entire story.