There’s a sort of arms race going on in TV. Writers are striving to find new and innovative ways to shock us jaded TV viewers so that we keep talking about their shows. Without, of course, straying over the clear guidelines for taste and decency that have been established by OFCOM.

And enforced by the large-print press.

The writers of Luther set their stall out early by opening this short series with one of the creepiest images ever shown in TV. A young woman had just got into her bed when a sinister figure slid, like some satanic car mechanic, out from underneath it.

There’s an image that would have 50% of TV viewers checking under their beds every night for weeks. The other 50% will of course, like me, have so many pairs of shoes, guitar cases and dust-covered board games under their beds that there isn’t enough room for even the slimmest serial killer. Us untidy people: we sleep very well indeed.

The basic concept of Luther is ‘The Sweeney meets The Silence Of The Lambs’. John Luther is a tough, dedicated copper. Just like his ancestor Jack Regan he isn’t afraid to bend the law if it means upholding justice. Just like Jack Regan he has a young sidekick who admires him, but also acts as his moral conscience.  Or at least he did.

Last week Luther fans were — I don’t know if ‘shocked’ is the word. We’re too desensitised to be truly shocked ever again — saddened, let’s say, by the death of Luther’s ‘George Carter,’ Justin Ripley.

A death at the hands of a man who is a baleful reflection of John Luther. The brutal avenger Luther might have become without Ripley’s steadying influence. A broadsheet-reading Batman who goes around taking down the nastier sort of criminals with extreme prejudice.

We’re too desensitised to be truly shocked ever again"

It’s the final episode tonight. And I mean final. There’s increasing certainty that there will be a feature-film outing for Idris Elba’s soft-spoken detective next year, but Luther’s television days are done.

And what that means, of course, is that it’s time for the writers to clean house. Extraneous characters that might clutter up a Luther movie will meet grisly ends. All those metaphorical guitar cases will come out from under the bed to make room for future serial killers. 

That Broadsheet Batman is still at large. He doesn’t seem to have run out of ammunition for his shotgun yet, and nobody’s thought to shut down his Twitter account. So no-one is safe.

Who’s for the chop? We’ll find out tonight. I can think of one character I’d like to see the back of. Two actually. You’re probably thinking of the same ones.

We’re terrible, aren’t we? Speculating about grisly murders. You know who’s made us like this? The writers of Luther. Thank God it’s over tonight.

I’m going to miss it.

The final episode of Luther airs on BBC One on Tuesday July 23 at 9pm. Episodes from this series are available on Catch Up on TV from BT.