Ben and Polly are still suspicious of the younger man claiming to be the Doctor, as the TARDIS lands on the colony world of Vulcan. The Doctor witnesses the murder of a newly-arrived examiner from Earth, and decides to assume the man's identity in order to investigate. He soon learns that a scientist named Lesterson has unearthed a crashed capsule containing the inert forms of three Daleks. The Doctor is horrified to discover that Lesterson has started reactivating them, intending to use them to serve the colony's populace -- ignorant of the fact that the Daleks have a far more sinister agenda.

Despite Patrick Troughton's initial misgivings about replacing William Hartnell in Doctor Who, on August 2nd, 1966 he signed a contract to play the new Doctor for a minimum of twenty-two episodes. Troughton's focus, as well as that of producer Innes Lloyd and story editor Gerry Davis, immediately turned to the way that he would portray the new Doctor. The production team had assured Hartnell that Troughton's take on the role would not simply ape his performance. Instead, it was proposed that the Doctor possessed the ability to periodically “renew” his body, transforming himself into a younger man. In this way, Troughton would be able to adopt his own approach to the role, without being beholden to aspects of Hartnell's portrayal.

During the ensuing weeks, Troughton found the process of creating the Second Doctor to be contradictory and frustrating. By the early autumn, the new incarnation was intended to have a sardonic sense of humour like Sherlock Holmes. The “renewal” undergone by the Doctor was noted as occurring roughly every five centuries, and was described as a terrible ordeal which forced him to relive all the dark moments of his past. The Doctor was still envisaged as a refugee from the destruction of his home planet during a galactic war, as had been postulated in early character outlines from 1963, and it was suggested that the new incarnation remained scarred by these experiences. Davis found himself drawing heavily upon Troughton's own characteristics; for example, the actor's love of dressing up prompted the notion that his Doctor would often wear disguises. Davis also took inspiration from the elusive manner of speech of James Stewart's eponymous character in the 1939 Western Destry Rides Again.

Sydney Newman argued that Patrick Troughton should play the Doctor as a “cosmic hobo”

For the Second Doctor's appearance, a number of wildly varying ideas were bandied about -- from blacking Troughton up like a character out of the Arabian Nights to giving him the silhouette of the Victorian politician Gladstone. Finally, Troughton was dressed as a Victorian-era windjammer captain and presented to Sydney Newman, the BBC's Head of Drama and a key figure in the original development of Doctor Who. Newman dismissed this approach, arguing that Troughton should instead play the Doctor as a “cosmic hobo”.

It was this description which inspired costume designer Sandra Reid to dress Troughton in a shabby echo of Hartnell's own ensemble. Even this would gradually be adjusted: the Doctor's comically baggy pants were slowly taken in, while his Paris beau hat was eventually discarded altogether. Likewise, it was thought that Troughton might wear a manic wig in the vein of Harpo Marx, but this didn't even make it into the studio. Co-stars Anneke Wills and Michael Craze protested that it would make the character impossible to take seriously, and so Troughton's own hair was instead given a tousled, unkempt style. It was the actor himself who suggested that the Doctor should carry a recorder, which he had learned to play while starring in 1960's Paul Of Tarsus. Newman's notion of a “cosmic hobo” had also put Troughton in mind of The Little Tramp, the beloved silent film character played by legendary actor Charlie Chaplin from 1914 to 1936, in movies like City Lights.

For his part, Innes Lloyd was very concerned that Doctor Who's audience would reject the change of lead actor. As such, he felt it would be prudent for the new Doctor's debut story to offer an additional reason for viewers to tune in, namely the programme's most popular monsters: the Daleks. Their appearance would also maintain the tradition, established during the last two years, of a Dalek story being broadcast in the lead-up to the Christmas holidays. The Daleks' popularity had faded from the heights of 1964, especially in the wake of their overexposure in the massive The Daleks' Master Plan a year earlier, but the monsters would still be firmly in the public eye following the August release of the Aaru Pictures movie Daleks: Invasion Earth 2150 AD.

Unfortunately, Dalek creator Terry Nation was unavailable to return to Doctor Who, due to his commitments as script supervisor on the action-adventure series The Baron. However, he indicated that he was amenable to another writer being brought in, and it was agreed that David Whitaker was a suitable candidate. Whitaker had been Doctor Who's original story editor, in which capacity he had overseen the first two Dalek serials; he had since worked with Nation on a variety of Dalek spin-offs. His most recent contribution to televised Doctor Who was The Crusade, written at the end of 1964, although another proposal, entitled “The New Armada”, had been rejected by Davis in January. On July 22nd, Whitaker was commissioned to write “The Destiny Of Dr Who”. In preparing his storylines, Whitaker consulted with Nation as to how the Daleks might best be utilised.

The draft scripts revealed that the Doctor had been “renewed” before

Around September, the serial's title became The Power Of The Daleks. Whitaker's draft scripts revealed that the Doctor had been “renewed” before; he was to open a drawer in the console which contained relics from his previous incarnations, including an earring and a metal bracelet. The scripts also specified the Doctor's age as 750 years, included various references to his grandchild Susan -- whose present location the Doctor could no longer recall -- and hinted that it might have been the Daleks who had destroyed his homeworld.

The director assigned to The Power Of The Daleks was Christopher Barry. Barry had most recently directed The Savages towards the end of the previous recording block, but had previously worked on their debut story, 1963's The Daleks. No new Daleks were constructed for the serial; instead, four Daleks were assembled and refurbished using the five casings retained by the BBC.

Production on the Troughton era began with filming at the BBC Television Film Studios in Ealing, London. Running from September 26th to 28th, this work chiefly concerned model shots and material set within the Dalek capsule. Also recorded on the last day was the climactic destruction of the Daleks, during which a stray spark from an exploding Dalek melted the nylon shirt being worn by operator Kevin Manser. It was during the Ealing filming that press photographers from The Observer captured images of operators Robert Jewell and John Scott Martin sitting in the bottom halves of their Dalek casings. The BBC was deeply unhappy with the subsequent publication of these pictures, as it comprehensively dispelled the popular myth that the Daleks were remote-controlled.

Troughton taped his first on-screen appearance as the new Doctor on October 8th, during the recording of the final episode of The Tenth Planet. The day before, however, Sydney Newman had indicated his unhappiness with how Whitaker had scripted the new Doctor; given the prolonged uncertainty regarding Troughton's approach to the role, Whitaker had tried not to define the character himself, instead writing generically. Unfortunately, Whitaker now had other professional commitments, while Davis was occupied with The Highlanders, which would be Troughton's second serial. On October 10th, Whitaker's agents agreed that another writer could be brought aboard to redraft the scripts, as long as their client retained the sole on-screen credit.

To this end, on October 12th, Dennis Spooner was formally approached about revising The Power Of The Daleks. Spooner had been Whitaker's successor as Doctor Who's story editor, and had also written half of The Daleks' Master Plan. Spooner's primary mission was to refine the portrayal of the Doctor, which he discussed with Troughton. In addition, Spooner found himself paring down Whitaker's overlong drafts, including the removal of an extensive sequence in Episode Three set in the colony's medical centre. Because of the extra time needed for Spooner to complete his work, it was decided that Doctor Who would take a one-week hiatus from studio recording; the delay meant that the cast would have to be paid for an extra week. Each episode would consequently be taped just two weeks before their broadcast, as had also been the situation for much of Season Three.

Patrick Troughton, Anneke Wills and Michael Craze soon forged a close camaraderie

At the start of rehearsals for The Power Of The Daleks, Anneke Wills and Michael Craze decided to prank their new colleague by dressing in t-shirts which proclaimed “Come back Bill Hartnell -- all is forgiven”. Troughton initially reacted badly to the joke, but the three actors soon overcame this misstep to forge a close camaraderie. Troughton found himself rapidly gaining confidence in his portrayal of the Doctor, and he began suggesting a variety of ad libs to add additional colour to his characterisation.

As usual, The Power Of The Daleks was recorded on consecutive Saturdays at Doctor Who's regular production home of Riverside Studio 1 in Hammersmith, London. Following the one-week pause, Part One was taped there on October 22nd. Hartnell was not required for the recording, and was represented by slide captions taken two weeks earlier. Unlike later changes of lead actor in the series' history, in this instance the Doctor's clothes were transformed along with his body, with his coat and hat later found after he rummaged around the TARDIS. The First Doctor's ring survived the “renewal”, but instead fell off the new incarnation's finger.

Both of Troughton's co-stars were given holidays over the course of the recording, with Wills absent from Episode Four on November 12th, and Craze from Episode Five on the 19th. The three regulars were reunited for the climax of The Power Of The Daleks on November 26th; unusually, this installment was captured on 35mm film rather than videotape, probably to assist the editing process. Two days later, on November 28th, a revised character outline for the new Doctor was issued, offering a more accurate description of the way in which Troughton was now playing the role.

Meanwhile, Episode One had been broadcast on November 5th; the era of the Second Doctor had officially begun. Although this episode earned an appreciation index of only 43%, the remainder of The Power Of The Daleks improved on this score, providing the first indication that Troughton's Doctor was finding favour with the audience. Indeed, this figure would prove to be a depth to which Doctor Who would never return.

• Doctor Who Magazine #180, 27th November 1991, “Archive: The Power Of The Daleks” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #4, 4th June 2003, “Good Vibrations” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #9, 2016, “Story 30: The Power Of The Daleks”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Second Doctor by David J Howe, Mark Stammers and Stephen James Walker (1997), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.