Doctor Who wasn’t the first television programme forced to recast a leading actor, but it was unusual that the change was commented upon within the series. Normally the audience would have just have to accept (or not) the recast and things would hopefully carry on as normal.

It doesn’t seem that having someone impersonate Hartnell was ever an option though – indeed, Troughton’s Doctor seems to revel in his differences. In the first episode the new Doctor is very playful – enjoying a tootle on his recorder whilst dancing a merry jig are two things you’d find it hard to imagine the Hartnell version ever doing.

It seems logical that David Whitaker returned to script this key story. Few people understood the genesis of the series as well as Whitaker – and this was important since briefly Doctor Who reset itself back to November 1963.

Back then, as now in November 1966, the Doctor is presented as an unknowable and mysterious figure whose thought processes are oblique. This means that his companions (now Ben and Polly, then Ian and Barbara) are the audience identification figures, which is a sharp reversal from the later Hartnell episodes which portrayed the Doctor as a fairly predictable figure.

Things kick off in part one rather oddly. Although Ben and Polly witnessed the Doctor’s transformation at the end of The Tenth Planet, Ben now struggles to accept that this stranger really is the Doctor. The way the Doctor now refers to himself in the third person (“the Doctor was a great collector, wasn’t he?”) and seems reluctant to answer a direct question only fuels his feeling of wariness.

Polly is quicker to trust him, but it’s not until episode two that the trio really begin to function as a unit, once they (and no doubt the audience) begin to understand that there’s method in the Doctor’s madness.

Kicking off with a Dalek story made good sense. And with Terry Nation unavailable, having Whitaker write it was also a sensible move as he’d written more about the Daleks than even Nation had – the TV21 comic strip, the first novelisation, The Curse of the Daleks stage play, etc.

Whitaker’s take on the characters was markedly different from Nation’s though. This would generate some friction in later years, with Nation commenting that he didn’t enjoy this story (feeling that the Daleks had been presented as too servile, which robbed them of their impact).

This criticism is slightly baffling and suggests that Nation hadn’t really studied the story in any detail. The plot of The Power of the Daleks revolves around the notion that since the Daleks are powerless to begin. patience is required from them.

In Nation’s scripts, the Daleks tended to be modelled on remorseless Nazi stormtroopers, blasting any and all opposition. Here this isn’t an option, so instead they pretend to be docile servants of the humans. It’s a long time before they speak, but their first words (“I am your servant”) repeated again and again at the end of the second episode casts a chill.

Even the later sight of a Dalek carrying a drinks tray – ostensibly the perfect servant – doesn’t really raise a smile as it’s undercut by the knowledge that eventually the Daleks will turn on their foolish human “masters”. The re-use of several of Tristram Cary’s music cues from the first Dalek story also helps in generating an oppressive atmosphere.

The Earth colony of Vulcan is a hot-bed of intrigue and revolt. The Governor, Hensall (Peter Bathurst), is attempting to maintain order whilst his second in command – Quinn (Nicholas Hawtry) – struggles to be kept in the loop. Bragen (Bernard Archard) is responsible for the base’s security and stalks the corridors following his own agenda whilst Lesterson (Robert James) is the scientist blinded to the danger that the Daleks pose. And it’s best to keep an eye on Lesterson’s assistant Janley (Pamela Ann Davey), who isn’t all she seems ….

There’s a lot to process within this diverse group of characters, so for once the six-part format feels just about right. The Power of the Daleks is one of those stories where every actor seems to be pulling their weight. Bernard Archard always had a sense of stillness and menace and even though we can’t see him, I think it’s likely that he was delivering. Peter Bathurst, later to reappear in a less rewarding role in The Claws of Axos, also gets a decent crack of the whip but the plum role has to be that of Robert James as the doomed Lesterston.

The misguided scientist is a familiar one in Doctor Who, but Lesterson is a particularly tragic case. He doesn’t seem to be motivated by personal glory or wealth, instead he simply sees the Daleks as a pliant labour-saving work force whose assistance will benefit everyone. But although he initially dismisses the Doctor’s warnings, over the course of the serial’s middle two episodes he slowly begins to understand their true nature. But by then he’s in too deep – not only pushed around by the increasingly confident Daleks but also manipulated by the cold-hearted Janley.

In an era when strong female guest roles were pretty thin on the ground, Pamela Ann Davy’s performance stands out (it’s noticeable though that she’s the only woman in the colony to be given a speaking role). Revealed to be in collusion with Bragen, the pair are plotting to take over the colony (with Janley pretending to assist the rebels in order that they can dispose of Hensall).

Unlike Polly, who has somewhat reverted to a damsel in distress (kidnaped and held captive for an episode, although this was a plot device to give Anneke Wills a week off) Janley is shown to be well able to run rings around her male counterparts. Although quite what she’s getting out of Bragen’s take-over is never quite made clear.

I love the scenes of black comedy featuring the Daleks in the middle episodes. For example, when one delivers a drink to Bragen and then returns a few minutes later asking if he’s finished or the way another Dalek has to bite its tongue after Lesterton tells it that it has an almost human interest and curiosity (all its willpower is required for it not to tell Lesterson that the Daleks are far superior!)

Unlike the slapstick scenes in The Chase, these moments don’t undermine the Daleks – instead they help to increase the tension that’s been slowly building throughout. And this tension continues at the end of episode four which climaxes with the newly built Daleks rolling off a production line in a nightmarish cliffhanger.

That’s also the point of the story where Lesterton finally loses his grip on reality. Robert James certainly doesn’t hold back at this point (offhand, I can’t think of many other performances of madness throughout the history of the series that are quite as extreme as this – even Graham Crowden’s cherished turn in The Horns of Nimon pales into insignificance).

Lesterson’s final scenes, in episode six, where he’s now quite calm but also quite mad, can’t help but chill the blood (for example, the way he parrots the Daleks’ oft-repeated “I am your servant” back at them shortly before they exterminate him).

The Power of the Daleks is streaked with cynicism. No previous story has ever displayed quite as jaundiced a viewpoint about the human race. We’re told that Hensall (murdered by the Daleks on Bragen’s instructions) was a good man and his deputy, Quinn, also seems to be on the side of the angels. But the story is really dominated by Bragen, someone who – in his own way – is nearly as ruthless as the Daleks.

Given this, once Bragen has finally murdered his way to the top job, you almost want the Daleks to begin running amok in order to turn his dreams into nightmares. They obligingly do this, although it’s interesting that Bragen dies by a human hand and not a Dalek one.

Although we only have the audio to go on, the massacre by the Daleks in episode six sounds relentless and unpleasant (it certainly makes any Dalek attacks in previous stories feel tame by comparison). That the Doctor defeats them seemingly accidentally is a neat touch – is he really just a lucky bumbler or does he prefer, at present, to keep his intelligence hidden behind a deliberately vague manner?

You couldn’t really ask for any more from Troughton in this one. Although the character of his Doctor has yet to totally emerge, he’s effortlessly established himself as the Doctor by the end of episode six. And with those arch scene-stealers, the Daleks, constantly lurking in the corridors, that’s no mean feat.

Is this the best Dalek story of all time? Yes, without a shadow of a doubt. 5 TARDISes out of 5.