Well, did you enjoy the return of LoD? Did you reckon it to be as brilliantly tense and twisty as ever, or did you think: OMG, WTF, SOS!? The show that spends all its time in deep cover got so enmeshed in polis-jargon acronyms at the beginning of its fifth run that I felt as if I’d been bashed around the head with Thandie Newton’s hacked-off arm from series four. “Is there a UCO embedded in the OCG that carried out the heroin hijack?” asked Vicky McClure’s Kate Fleming. It was a reasonable question but not one I could answer. The brain was birling with so many big capital letters jammed together. So much so that I’d forgotten what CCTV stood for. I’d even forgotten that PC also meant police constable. But here’s what a drama can do when it’s this good and knows it. It can tell its audience: “We are fearless, we know no limits, keep up.” And this pulverising start, the most shocking yet with three police officers ambushed and slain in a baby-in-peril scam, may have been Line of Duty telling the BBC: “See when you trailed us as being ‘From the makers of Bodyguard’? We’d like to remind you that we’re the senior series and don’t need to rely on shots of Richard Madden’s bare bum to get the whole nation talking.” Jed Mercurio created both thrillers of course and for the reunion of Fleming, Steve Arnott (Martin Compston) and Ted Hastings (Adrian Dunbar), TV’s pre-eminent dramatist gave us some early, edgy glances through glass walls and across desks to remind us that no one can trust anyone around here. “Here” is AC-12, the unit which polices the polis. In the first years of Line of Duty I used to say: “This is good, but of course Between the Lines got in first with tales of bent coppers.” Now, though, it’s left the rival far behind. BtL never dared suggest that the anti-corruption boss might be the most bent of them all. The star guest this time is Stephen Graham, a killer at the outset of the episode revealed to be a (gulp) polisman at its end. Is he Balaclava Man? Well, his entire gang were similarly attired – we’ll clearly all be wearing the sinister woolly headgear next winter – and there’s also a Balaclava Woman. Who is the mysterious H? Hieronymus Bosch? Heffalump? Herman of those Hermits? Last time out I refused to believe Hastings was the baddest apple. Last night it seemed possible until he came up against DS Alison Powell (Susan Vidler, grew up in Cockenzie, East Lothian, uttered one of Trainspotting’s unforgettable lines). Normally Hastings doesn’t take snash from anyone but he was told by Powell he’d stumbled on an undercover operation – “and now I need you to stumble away”. Basically, AC-12 had been thwarted in its investigation into ED905 by a C1601. H could still be Hastings but having hinted at this already the mercurial Mercurio is surely not going to allow us to have solved the infernal puzzle with five more instalments (and probably at least another series after this) to come. Similarly we should be wary of Graham having been fingered as the right bad yin this early. I mean, he’s organised the murder of three officers. He’s sitting on a lorryload of heroin. He hangs around a godawful nightclub. But in the strange, warped, claustrophobic and utterly addictive world of Line of Duty there could be a perfectly good excuse for all of this. TBC (to be continued – come on, get with the beat).