Last night's viewing: Line of Duty, BBC2; Imagine, BBC1

Even if you didn't see the opening sequence of Line of Duty last night you'll still have seen it. That's because we've all seen it a hundred times before – the operational prelude to a police procedural with urgent radio calls and stressed men saying things like, "Bravo. Are you visual?", and armed officers on a crouching run to flank a door.

But then, in the middle of this flurry of clichés, you're suddenly hit by something you didn't expect. One of the radio transmissions doesn't fit the template: "We need you to complete the Risk Assessment," says a steely voice, "we need that paperwork!" "Done," replies Steve authoritatively. Unfortunately, he's just about to discover that he failed to adequately assess the risk that a loosely attached door number would convert Flat 56 into Flat 59.

The raid goes horribly wrong, leaving an innocent man dead, and Steve's reluctance to go along with the subsequent cover-up sees him seconded to an anti-corruption unit, where he's given the task of investigating DCI Anthony Gates. On this evidence at least, Gates lives a life of startling dramatic compression. His day begins with a quick cup of coffee with his mistress, interrupted by the rescue of a young mother from two knife-wielding muggers, continues with the reception at which he receives his Officer of the Year award, detours briefly so that he can help his mistress cover up a drink-driving incident and ends with him kissing his sleepy wife at home. Why didn't she go to the award reception with him, you wonder? If you continue to ask these helpful questions, I may have to ask you to leave.

The anti-corruption squad think that DCI Gates is just too good to be true – a suspicion that may also have crossed some viewers' minds by now. And although the only thing they can pin on him for the moment is failing to declare the free coffee given to him by an admiring waitress, they have their suspicions that he's been "laddering" – cherry-picking his cases to ensure that his clear-up rates are stellar. Meanwhile, his mistress's little accident has got more complicated; she may have killed a man and Gates finds himself tampering with evidence under the very noses of detectives who are meant to prevent that kind of thing.

The thriller material has already set its hooks solidly. But Jed Mercurio has added to it two themes that promise to thicken and enrich the relatively thin pleasure of not knowing who's done what to whom. The first is racial politics. "Nobody's blacker than me, son," hisses Steve's boss furiously, when the latter has suggested that DCI Gates might have had to try harder to achieve his rank than a white officer. In his eyes, a stint as a Catholic policeman makes him victim not victimiser. The second, hinted at in that opening sequence, is the interplay between bureaucracy and policing, and the ways in which the paper trails of accountability can easily distort what crimes get solved and how. Making form-filling into edge-of-the-seat stuff won't be easy, but with this cast and this writer it could happen.

"It's a massive mountain to climb," said Alan Yentob near the beginning of Imagine, a phrase presumably designed to reassure us that Chris Terrill's film would cleave to the dog-eared blueprint of challenge and triumph that deforms so many documentaries these days. I nearly switched off right there but I'm glad I didn't because what followed was very affecting, an account of badly injured soldiers creating a theatre piece out of their own experiences and trauma. At times, the project was in danger of aggravating the very problems it set out to describe – opening up semi-healed wounds. But it also seemed to restore as well: "Go out there and slay 'em," said the director before sending them over the top. And they did.