Did Luther get a job lot from Harvey Nicks? It would certainly explain why he has no money left to spend on interior decorating. Although his new residence is a step up from the squat horror of his previous flat, it would still give Kevin McCloud palpitations if he ever set foot inside.

There’s plenty of satisfying tachycardia for everyone else as well – the moment nurse Jodie reaches up to the top of her wardrobe for a towel, unaware a crazed killer is watching her from inside, is petrifying – although perhaps not quite as much as last week; this instalment is more about resolving the story than scaring the crap out of us.

We meet the Shoreditch Creeper (not an item of soft-soled hipster footwear but William Carney: a retired murderer who resembles an elderly Withnail gone rotten) and learn his connection with present-day psycho Paul Ellis. It’s a toss-up as to which is the most repulsive, with Carney (Ned Dennehy) drooling over photos of his protégé’s prey and Ellis (Kevin Fuller) disguising himself as Hank Marvin to evade detection, but the latter just shades it by sticking three toothbrushes (all belonging to other people) in his mouth at the same time. Horrific.

Thankfully, Luther (Idris Elba) has the measure of both of them – and of DSU George Stark (David O’Hara). ‘If you take me down,’ Luther promises his gravel-and-Glenmorangie-gargling nemesis, ‘I’ll take you down even faster and even harder.’ In the end, though, he simply strolls out of the Complaints’ shabby basement HQ (‘Secret Squirrel Central Station’, as he dubs it) with a folder of evidence and a tape of DS Ripley’s testimony against him.

Stark is left tearing down his Luther Porn Wall™ in a rage while Ripley (Warren Brown) looks as awkward as someone with flatulence at a funeral. Yet when Luther listens to the recording, he discovers his estranged friend has praised him to the rafters and slated Stark’s investigation as ‘little more than a fishing expedition and a witch hunt’.

If this sudden change of heart from Ripley seems difficult to believe after last week, it’s only because his betrayal of Luther was pretty far-fetched in the first place. The spiky and frequently self-conscious friendship between the two detectives is one of the few entirely realistic things in a series which is at its most likeable when being unlikely.

Aired at 9pm on Tuesday 9 July 2013 on BBC One.

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