On paper, this week’s episode of Being Human may not have looked too promising. A mash-up of J. B. Priestley, Rentaghost and 1970s child safety advertisements? Really?

But as it happens, Tom Grieves’ A Spectre Calls – even the title is perfect – is a thing of glory: an episode that constantly treads the line between creepy and funny thanks, in no small part, to the central performance of James Lance as Alfie Kirby.

Part kipper-tied Pied Piper, part self-appointed self-help guru, Kirby has a mean line in passive-aggressive manipulation and all the creepiness of an over-familiar children’s television presenter. It’s no surprise that he tries to come over all Dave Prowse, as he fatally re-enacts the Green Cross Code advert in what is the first of many cringe-out-loud scenes.

This is a man who identifies with the child safety police of the Seventies – who casts himself as both Starksy and Hutch – but whose ability to make a modern audience squirm is like David Walliams on speed-dial.

You can tell he’s a man of the ’70s: no man nowadays would consider it the way to a woman’s heart to style themselves as the nursery teacher with special responsibility for sick. They’d surely be dumped quicker than you can say ‘child protection’. But Kirby is an infantilised figure himself – a Peter Pan of spooks who whispers a GP to death in a moment of almost fetishistic intimacy.

If Kirby is able to appeal to Tom’s inner child, it’s only because he knows all about arrested development.

True, for this particular sub-plot to work, it means that other aspects of Tom’s character must be parked to one side: his capacity for vengeance and his killer instinct. It may feel like a regressive step for the character to become so suddenly boyish. But there’s a logic to it, too: this is the closest Tom has ever come to having a family structure, and his first chance to act out the childhood he never had.

In fact, it’s the genius of Kirby that he is a twisted mirror to all the leads, who, in recognising their secrets, is able to use these against them. With Tom, it’s the common desire for a family. With Hal, it’s the dark desires of the serial killer. And with Annie it’s the broken ego of the person who considers themselves unlovable. When Kirby finally turns on her, he knowingly re-enacts her abusive relationship with her fiancé and murderer, Owen… then busts some serious John Travolta moves. In a tank top.

In a programme which routinely portrays the torments of the damned, it’s still rare to find a character who has sacrificed so much of their humanity they might genuinely be capable of anything.

But, as Kirby describes the manner in which he ingratiated himself in the homes of his child targets, it comes as a heart-stopping relief to hear that his crime is only the multiple homicide of adults. For more than a moment there, we were convinced the episode was heading down a very dark path indeed.

Still, there are plenty of laughs too, and, whether it’s Tom’s curious stand for LGBT rights or Hal’s absolute inability to embrace his inner gay, there’s a deft wit to the script which allows the actors to exercise their comic muscles.

As Hal awkwardly perfects his gym queen look or takes a decidedly un-Zen approach to his daily workout, it gives us the opportunity to check out one thing – and it’s not what you think. It’s confirmed that, yes, indeed, there is no burn mark on Hal’s arm at the start of the episode. So what happened between the time when he was forced out of Honolulu Heights and when he returned must now be a matter for conjecture.

Doubtless, Woman in the Future who May or May Not Be the Adult Eve ™ will have the answers. But frankly, we’re already a bit bored with her technology-invading appearances.

The programme currently has three such engaging leads that it simply doesn’t need a voice in the machine going all portentous on us. As far as the overarching plot is concerned, it may be All About Eve, but after tonight’s episode, we’re more than content with Alfie.

Aired at 9pm on Sunday 26th February 2012 on BBC Three.

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