On the desert planet Aridius, Ian and Vicki go exploring while the Doctor and Barbara enjoy the sun. However, the companions are unaware that the Daleks have constructed their own time machine, and are determined the hunt down the TARDIS. The Daleks land amidst a terrible sandstorm, forcing the Doctor and Barbara to seek help from the native Aridians in locating Ian and Vicki, who are menaced by terrible Mire Beasts. But Aridius is just the first stop in a desperate chase through time and space, which will lead to the Empire State Building, the Mary Celeste, a haunted house, and beyond.

Even before The Dalek Invasion Of Earth started airing in November 1964, writer Terry Nation was already discussing a further adventure with the Doctor Who production team. On October 6th, incoming story editor Dennis Spooner -- a friend of Nation's from the Associated London Scripts co-operative -- commissioned him to write a six-part story which was expected to conclude the programme's second production block. When the decision was made to re-edit the third and fourth installments of Planet Of Giants into a single twenty-five-minute episode, thought was briefly given to extending Nation's storyline to seven parts as compensation.

By mid-December, however, Nation's idea was abandoned and, on December 16th, he was commissioned to write a new six-episode Dalek serial in its place. It was accorded the functional title of “The Daleks III”, and took the place of the abortive storyline in the production schedule. Early in 1965, an additional nine episodes were allocated to Doctor Who's second recording block. These would comprise a four-part story that would now form the Season Two finale, together with five episodes that would be held over to lead off Season Three. As such, Nation's scripts would now form the second season's penultimate adventure.

One of the story's goals was to introduce a major new monster: the Mechonoids

By early January, Nation's serial had gained the working title “The Pursuers”. The Dalek time machine at the heart of the narrative was referred to by Nation as a “Dardis” (ie, “Dalek TARDIS”), although this term was never used on-screen. As with the Zarbi in Bill Strutton's The Web Planet, which was then in production, a goal of the Dalek story was to introduce a major new Doctor Who monster. In “The Pursuers”, these creatures were originally called Mechons, later changed to Mechonoids (although their name would be misspelt “Mechanoid” in the closing credits, and on subsequent merchandise). Their planet was first known as Mechon as well, and then became Mechanus.

The denizens of Aridius (originally Aridus) were envisaged as ugly, hunchbacked creatures. Nation's drafts initially introduced the Fungoids on Aridius, as opposed to confining them to the Mechanus sequences. The Doctor's explanation of the haunted house existing in a realm of human thought was in fact Nation's concept for the segment, which producer Verity Lambert feared would undermine the programme's narrative reality, and imply that Doctor Who had already run out of ideas to the point of cribbing other writers' villains. Baron Frankenstein was at one point included in these scenes, while the Grey Lady was a late addition. Bizarrely, Nation gave Vicki a panic attack during the roof escape from the Mechonoid city, requiring Barbara to knock her unconsciousness with a punch to the jaw!

Dennis Spooner was keen to provide more links from one serial to the next, and so he added the element of the Time-Space Visualiser to both Nation's storyline and the preceding adventure, The Space Museum. At one stage, this was called the “Time Curve Visi-Scope” and was an invention of the Doctor's. The Visualiser scene originally depicted the time travellers watching a speech by Winston Churchill, instead of a performance by the Beatles. At one point, Shakespeare's wife, Anne Hathaway, appeared as well. Spooner also simplified the action on Aridius: Nation had envisaged an entire colony of mire beasts who dragged Ian and Vicki below ground, while Spooner's revisions required just a single mire beast and added the trap door access to the tunnels.

It appears that “The Pursuers” was abandoned as a title by late February, and the scripts became known simply as “Dalek Three”. In the spring, the adventure was rechristened The Chase. Along the way, Nation discarded several additional ideas, including sequences set in ancient Egypt (where the first of the Great Pyramids would be erected over the remnants of a destroyed Dalek), on the planet Stygian whose inhabitants were invisible, and on the mist-shrouded world of Vapuron. These concepts would subsequently be revived for The Daleks' Master Plan.

The new companion was an astronaut originally named Roger Bruck

The contracts of both William Russell and Jacqueline Hill were due to expire with The Chase and, during the early months of 1965, both actors indicated that they were considering leaving Doctor Who. While it was felt that there was no need to preserve an adult female character, Ian's role as the heroic male was deemed indispensable. Nation was therefore asked to include a new adult male in his scripts who could become a regular character; this was an astronaut named Roger Bruck. Due to the uncertainty surrounding the lead cast, Nation elected not to write the final scenes of The Chase himself, instead leaving it to Spooner to determine the fates of Ian, Barbara and Roger. Around early May -- by which time it was known that both Russell and Hill would indeed be leaving Doctor Who -- the new companion became known as Michael Taylor.

Since The Chase had significant requirements for props and sets, two designers were assigned: John Wood and Raymond Cusick. Cusick, who had created the Daleks' visual appearance for their debut story, was unhappy with the modifications made by Spencer Chapman on The Dalek Invasion Of Earth, and had them removed. These included a radio dish to explain why the Daleks were no longer reliant on static electricity -- which Cusick replaced with vertical solar panels positioned between the head grille and skirt sections -- and larger fenders.

The two original Daleks donated to a Doctor Barnardo's Home were unavailable for The Chase, and so Shawcraft Models was asked to construct one new Dalek casing. This was a pared-down version with limited features, which would largely be used for sequences involving a significant chance of damage (for example, this was the Dalek buried in the sand on Aridius). As such, a total of five regular Daleks would appear in the new serial. Their numbers were amplified by three Dalek casings made for the Aaru Pictures film Dr Who And The Daleks, which had recently finished production. The Aaru Daleks differed considerably from their television counterparts, and so they underwent some modification (such as by having their fenders removed to offset their greater height). As such, they were used only in the background of some scenes.

Christopher Barry, the director who had introduced the Daleks in The Daleks, was considered for The Chase. In the event, however, the job went to Richard Martin, who had been involved with both previous Dalek stories, and who had recently completed The Web Planet. Martin was growing wary of being too closely associated with Doctor Who monsters, and with the Daleks in particular; while Verity Lambert successfully persuaded him to return for The Chase, it would be his final contribution to the programme.

Production began on April 9th with a day's location filming at Camber Sands, a beach at Camber in East Sussex, which doubled as the surface of Aridius. Originally, it was hoped to realise the scene where a Dalek levitated out of the sand by burying a Dalek casing in a dune and then pulling it out on a rope attached to a Land Rover. Unfortunately, when the shot was attempted, it was found that the weight of the sand kept the Dalek pinned firmly in place. The sequence was instead performed as a model shot at the BBC Television Film Studios in Ealing, London. Work there spanned April 12th to 15th, and also included the Lincoln and Shakespeare sequences which would appear on the Time-Space Visualiser, the Mary Celeste scenes (which marked the first use on Doctor Who of the water tank at Ealing), and the battle between the Daleks and the Mechonoids.

In between, on April 10th, the Beatles recorded a performance of their new single Ticket To Ride at Riverside Studio 2 in Hammersmith, London. This footage was intended for the April 15th edition of Top Of The Pops, but permission had been obtained for a clip to be used in The Chase as well. It was a considerable departure from Nation's original idea, which was to depict the band performing at a fiftieth-anniversary concert, with the Fab Four dressed up as old men. It appears that the Beatles themselves were interested in the proposition, but it was vetoed by their manager, Brian Epstein. Ticket To Ride replaced an earlier suggestion that a November 1964 recording of I Feel Fine be made available to the Doctor Who team.

The first episode of The Chase, The Executioners, was recorded on April 30th; as usual, all six installments were taped on Fridays at Riverside Studio 1. On May 6th, Douglas Camfield (who had recently directed The Crusade) and a stills photographer accompanied William Russell and Jacqueline Hill on an excursion to several London landmarks. Their objective was to capture images which would comprise the final episode's montage. On May 10th, as part of pre-filming for The Time Meddler, Camfield also supervised the London bus segment at Ealing, as well as Ian and Barbara's return to 1965, which was recorded at the Film Studios' maintenance garage.

Part three, Flight Through Eternity, was recorded on May 14th. The guide played by Arne Gordon, unnamed on-screen, was referred to in some documentation as Henry de Voort. When making The Web Planet, Martin had declined to cast actor Peter Purves as a Menoptra, but had promised to find him a better role. This turned out to be the obnoxious American tourist Morton Dill in Flight Through Eternity. Purves proved popular with the cast and crew, several of whom recommended him to Verity Lambert for the part of the new companion, Michael. Lambert and Spooner concurred, and offered Purves the role later that night.

On May 21st, Peter Purves was formally contracted for 13 episodes

Purves spent the next week working with Spooner to better define the character; it was during this process that his name was changed to Steven and he acquired his toy panda, HiFi. On May 21st, Purves was formally contracted to play Steven Taylor for thirteen episodes -- through the first story of the next recording block (ultimately The Myth Makers). On the same day, Maureen O'Brien received a contract extension covering the same period. Then, on May 24th, William Hartnell was retained through the midpoint of Season Three (the serial that would become The Celestial Toymaker).

In episodes four and five, Edmund Warwick joined the cast to double for Hartnell in scenes involving both the real Doctor and his robotic doppelganger. According to Warwick, this part was written especially for him, as thanks for his help filling in for Hartnell when the series star was injured during the making of The Dalek Invasion Of Earth. Given that Warwick only vaguely resembled Hartnell, it was decided that Warwick's appearances would be confined to long shots, and that Hartnell's voice would be dubbed over any of his lines. Despite this, one piece of dialogue was inadvertently transmitted in Warwick's voice. Unusually, the May 28th recording of the fifth episode, The Death Of Doctor Who, began in the afternoon rather than the evening. This was done so that the sequence of the Doctor fighting the robot could be completed separately from the rest of the installment, in consideration of how physically taxing the material would be for Hartnell to perform.

The Planet Of Decision, recorded on June 4th, saw the return of Purves, now playing Steven Taylor. But while one character was joining the ranks of Doctor Who's recurring cast, the Mechonoids were establishing themselves as a one-off creation. Their unwieldy, bulky design made them very difficult to use effectively, especially in the limited confines of the recording studio. Like the Zarbi of The Web Planet before them, the Mechonoids would endure primarily in Doctor Who spin-offs, such as the Dalek comic strip in the pages of City Magazines' TV Century 21 weekly publication, rather than in the programme itself.

This was also the final day on Doctor Who for both Russell and Hill. Hartnell was particularly upset about their departure, which left him as the last of the original regular castmembers remaining on the show. Because Spooner was needed to write the next serial in production, The Time Meddler, The Planet Of Decision was also the last episode on which he was credited as story editor. In principle, Spooner handed the job over to Donald Tosh at this stage; Tosh had been trailing him throughout the production of The Chase. However, Spooner would continue to perform uncredited story editing on Doctor Who for several more weeks.

The BBC announced Peter Purves was joining Doctor Who just a week before Steven Taylor made his on-screen debut

It was not until June 18th that the BBC announced Purves was joining Doctor Who -- just a week before Steven made his on-screen debut. Small changes were made to the BBC1 Saturday night schedule on several occasions during the broadcast of The Chase. Episodes two and five both had cricket highlights inserted after the news update which usually came between Doctor Who and The Dick Van Dyke Show. Ian and Barbara's farewell on June 26th, meanwhile, gave way not just to the news and weather, but also to forty-five minutes of Wimbledon tennis coverage, with the ongoing misadventures of Rob and Laura Petrie pushed back to later in the evening.

Meanwhile, the broadcast of The Chase part one was discussed four days later, at the May 26th meeting of the BBC's Programme Review Board. There, the Controller of Programmes for BBC Television, Huw Wheldon, observed that Doctor Who was not taking sufficient advantage of the Daleks' enormous popularity. When informed that a fourth Dalek serial was being planned for the autumn, Director of Television Kenneth Adam indicated that its length should be more than doubled, from six episodes to thirteen. The British public's appetite for the mutants from Skaro was about to be tested like never before...

• Dalek 63·88, edited by Jon Green and Gavin Rymill.
• Doctor Who Magazine Summer Special 1993, “Archive: The Chase” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “I'm Into Something Good” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #5, 2016, “Story 16: The Chase”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The First Doctor by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.