The rules of television are as follows.

Rule 1: David Tennant must be in everything. Rule 2: Olivia Colman must be in everything. Rule 3: never try to do the same thing twice. Series two of Broadchurch (Monday, STV, 9pm) obeys the first two rules (and is very good because of it) but blatantly breaks the third one and, over the next seven weeks or so, will probably get away with it.

You may remember that the first series in 2013 ended with the revelation that Joe Miller, the seemingly nice hubby of Olivia Colman's police-woman character Ellie Miller, was in fact the killer, although from the beginning, the whodunnit element was never the most important part of the series. Indeed, the writer Chris Chibnall did not even decide until well into the writing process who was going to be the killer; it could just as easily have been someone else.

Much more important was the stress of what the killer did and how those events affected people and deflated, diluted and dissolved them. It's a subject which is a sideline in most whodunnits, but Broadchurch moved it from the side to the centre and it's even more important in series two. David Tennant, poor lad, is particularly doom-laden and weighed down by the strain and stress of everything - he is worried and painfully thin, like a piece of paper dangled over a shredder.

There was one thing, however, that the second series could never do again which is to explore, as the first series did so well, the compelling, disturbing idea of what respectability hides: the idea that under the clean, freshly-scrubbed skin of every community is a collection of fleshy organs, pumping corruption, distrust and deception. Seeing Chibnall peel the skin back in the first series was its greatest disturbing joy and, as the murder trial got under way in series two, Joe Miller alluded to it again when he said to his lawyer, grumpily, threateningly: "Nobody's innocent. Everybody's hiding something."

Chris Chibnall is clearly still in love with this idea as an inspiration for drama and has introduced some intriguing new characters to explore it further, including a lawyer played by Charlotte Rampling with laser eyes and a Bensons and Hedges voice. Chibnall's great skill is to capture the banal drama of his characters' conversation without ever resorting to cliché, something which he has learned from loving television for a long time.

About 30 years ago, when he was just a boy, Chibnall appeared on a BBC discussion programme called Open Air and criticised the way television was written. It was unchallenging, he said, it rarely offered an alternative to the norm, and it was often clichéd. At the time, in the 80s, Chibnall hadn't yet written a word for television himself, but he was right and in the 30 years since he has been part of a great improvement in the way TV is commissioned, created and written. Television has moved from it early stagey days when it was essentially TV cameras pointed at the theatre to what it is now: TV cameras pointed at real life. And Broadchurch is one of the finest moments of that change for the better.