1980s script editor Andrew Cartmel recounts a story of how, in his early days of working on Doctor Who, he suggested to producer John Nathan-Turner the use of a tentacled monster. Apparently JN-T said with world weary experience, ‘tentacles are difficult’.

Twenty years later, he was proven right when this lurid two part story featured a human Dalek hybrid as its main villain. An intricate mask of make up and prosthetics transforms actor Eric Loren into a man with a Cusick style Dalek mutant for a head. Unfortunately it also has a series of tentacles which twitch awkwardly throughout proceedings, and look unfortunately phallic. This guy, he’s quite the dickhead.

The image of Dalek Sec, in his pin striped suit and black and white shoes below his scaly one eyed doodle face, dominates Daleks in Manhattan/Evolution of the Daleks. But it shouldn’t overshadow the interesting themes running through the story. Writer Helen Raynor mashes up the Daleks with depression era New York, and body horror with song and dance, to pose questions about human nature. It’s an unusual combination of elements, but it’s the most innovative take on a Dalek story since 1967’s The Evil of the Daleks, with which it shares a focus on the dividing lines between humans and Daleks.

The theme is established early through the character of Solomon (Hugh Quarshie), named (not very subtly) after the biblical king, whose wisdom was evoked in the story of the two mothers who claimed one baby. Here, he similarly mediates in a fight between two men over a loaf of bread. “No matter how bad things get,” he scolds them, “we still act like human beings.”

Things get pretty bad for young hot potato Laszlo (Ryan Carnes) who, early in the story, is turned into a hybrid pig slave. Once considered comely, he now has a face only his devoted showgirl Tallulah (Miranda Raison) can love. Unlike the legion of other pig slaves, Laszlo hangs on to his humanity, and is a constant reminder of what Solomon was saying.

On the other end of the spectrum is the ruthless foreman Mr Diagoras (named, it seems, after an ancient Greek atheist). He’s supervising the construction of the Empire State Building, and is pushing his workers to their limits, knowing their desperation for paid employment in the middle of the Depression. Diagoras’ masters are the Daleks, and they are pleased with him. “You think like a Dalek,” one of them says to him. And soon enough, he’ll have functional appendages like one too. And not so functional ones hanging from his face.

So the story is peppered throughout with characters talking about – or pushing the boundaries of – what it means to be human or Dalek. This leads to the reveal of Dalek Sec’s big plan, the hybridization of himself with a human being. The trouble is, this goes against his troops’ deeply ingrained instincts towards racial purity. As a result, we get something very rare: a Dalek/Dalek argument.

DALEK THAY: This action contradicts the Dalek Imperative.

DALEK JAST: Daleks are supreme. Humans are weak.

DALEK SEC: But there are millions of humans and only four of us. If we are supreme, why are we not victorious? The Cult of Skaro was created by the Emperor for this very purpose. To imagine new ways of survival.

DALEK THAY: But we must remain pure.

DALEK SEC: No, Dalek Thay. Our purity has brought us to extinction. We must adapt to survive.

Post transformation, Dalek Sec initially finds what he desires from the human part of himself: ambition, hatred and aggression. “This species is so very Dalek,” he savours, like a connoisseur sipping a new wine. Predictably enough though, Sec starts to exhibit qualities such as mercy and humility, to such an extent that his Dalek compadres can no longer take it. In my favourite scene, two Dalek conspirators sneak off into the sewer and admit their doubts about Sec’s plan to each other. One’s head swivels around 180 degrees to check they’re not being eavesdropped upon. That bit never fails to raise a smile; this species is so very human.

From then on it’s only a matter of time until they turn on old penis features. They don’t simply exterminate him (they never do when it’s someone important). They chain him by the neck and force him to walk on all fours. He gets to die sacrificing himself for the Doctor, the first Dalek to ever do so. And the Daleks return to their villainous status quo.

This is the ultimate problem with a story like Daleks in Manhattan, or indeed The Evil of the Daleks, or any story that tries to do something new with the Daleks. They are the least flexible component of Doctor Who. If you try to alter them, they have to be reset to their original monstrous state. They can’t be changed.

A separate, more morally ambiguous strain of Daleks, perhaps even with newly designed casings might be a very interesting development for Doctor Who. I doubt it will ever happen though. Remember the outrage when there was an attempt to update the Dalek design in Victory of the Daleks (not to mention what the Nation estate would have to say). They can’t be touched, literally or metaphorically.

Where this inevitably leads us, is to the need for Davros. He’s the one great innovation in the Daleks. When introduced to the series in 1975, he provided the impetus for the next four stories. Even in the new series, he periodically pops up to liven things up. And look, the next Dalek story after Daleks in Manhattan sees his return. Because he’s a character which can add that element of unpredictability to the Daleks. Dalek Sec had the potential to be another recurring character in the Davros mould; someone who could have been the spark that lit some new fire under the Dalek mythos.

But can you imagine being confronted with those spasming face cocks every time he turned up? No. Just no. Haven’t we learnt? Tentacles are difficult.

LINK TO Bad Wolf/The Parting of the Ways. I don’t have to point this out, do I?

NEXT TIME: Unhand me, Madam! It’s more trouble with tentacles in Spearhead from Space.