When the secret plans to a disintegrator gun are stolen by what appears to have been some kind of giant robot, the newly-regenerated Doctor is quickly called in to investigate. The trail leads to a group of right-wing scientists at the Thinktank facility, who are seeking to use the robot and the disintegrator gun to impose their edicts on humanity. As the situation escalates, Sarah Jane may prove to be the Doctor's only means of influencing the robot.

As Doctor Who's eleventh production block neared its conclusion in 1974, the programme was in a state of flux. Although Planet Of The Spiders was to mark the end of Jon Pertwee's tenure as the Doctor and form the final serial of Season Eleven, the recording block would continue with the Fourth Doctor's introductory adventure, which would be held over to start the programme's twelfth season in the autumn. Outgoing script editor Terrance Dicks, who was concluding his work on Doctor Who with the Pertwee swansong, saw this as an opportunity to quickly secure a contract now that he had returned to the ranks of freelance writing. Dicks convinced his replacement, Robert Holmes, that the programme had a tradition of departing script editors being commissioned by their successors, and so he was assigned the task of writing Serial 4A. (Dicks was formally contracted much later, on May 23rd.)

At this stage, the new Doctor had yet to be cast, but Dicks and producer Barry Letts -- who would himself be leaving Doctor Who at the end of the recording block -- were seriously contemplating casting an elderly actor in the role. They decided that this would necessitate the introduction of a new character who would be able to handle the physical aspects of the storylines, in the vein of Sixties companions such as Ian Chesterton and Jamie McCrimmon. Letts and Dicks therefore created a UNIT surgeon named Lieutenant Harry Sullivan (after possibly considering the surname Sweetman) to accompany the Doctor. Although UNIT was being gradually deemphasised, it was felt that Harry would also provide an enduring link to the organisation, thereby adding a familiar element to the new Doctor's adventures.

To play Harry, Letts cast Ian Marter. Marter boasted a hefty resume of stage appearances, as well as roles in television series such as The Brothers and Play For Today. Marter had already appeared in Doctor Who as John Andrews in Carnival Of Monsters more than a year before, and had been Letts' initial choice to play the recurring role of UNIT Captain Mike Yates. Marter and Elisabeth Sladen were both issued 26-episode contracts on April 16th -- even though by this point, the “elderly Doctor” concept had been discarded and Tom Baker cast in the lead role, making Harry somewhat redundant.

Work on the character of the Fourth Doctor proceeded in earnest throughout the month of March. Joining the team by this point was Doctor Who's incoming producer, Philip Hinchcliffe. Hinchcliffe had gotten his start in television as a script editor for ATV, and eventually attained the position of associate producer on programmes such as General Hospital, Crossroads, and various children's shows. It was ultimately agreed that Baker would play the Doctor as more of an eccentric than Pertwee's prototypical man of action, playing up the fact that, as an alien, the Doctor's thought processes and reactions could sometimes be a departure from the human norm.

Drawing upon the bohemian tendencies suggested by both Baker and Letts for the Fourth Doctor, costume designer James Acheson put together an outfit which unconsciously echoed the 1892 Aristide Bruant lithographs of Henri de Toulouse-Lautrec. To knit the scarf he intended the Doctor to wear (one of the elements inspired by Toulouse-Lautrec), Acheson approached an elderly woman named Begonia Pope. Misunderstanding Acheson's instructions, Pope used all the wool given to her, resulting in an inordinately long scarf. Baker, however, liked the image this conveyed, and although its length was reduced slightly, it was felt that the scarf could be incorporated into the action and make an effective prop.

Dicks, meanwhile, had been working on his scripts in consultation with Holmes. The new script editor was interested in a story which considered how an advanced, autonomous computer intelligence might behave, while Dicks was interested in writing about a sympathetic monster, inspired by the 1933 film King Kong. Dicks also drew heavily on The Mauritius Penny, an episode of The Avengers he had cowritten with Malcolm Hulke, most notably for the scenes in which Sarah Jane infiltrates the meeting of the Scientific Reform Society. Calling the adventure Robot, Dicks incorporated several hallmarks of the Pertwee era to reassure audience members. These included the roadster Bessie and the characters of Brigadier Lethbridge Stewart and Benton (now promoted to Warrant Officer so that he could replace Captain Yates as the Brigadier's second-in-command); Nicholas Courtney and John Levene were issued contracts for Robot on April 17th.

The director assigned to Robot was Christopher Barry, whose last Doctor Who work had been on The Mutants two years before. Unusually, Barry elected to conduct all location recording using videotape rather than the traditional film, due to the heavy use of the Colour Separation Overlay technique required to achieve the effect of the “giant” robot in episode four. All exterior shooting was conducted at the BBC Engineering & Training Centre at Wood Norton, Hereford and Worcester, from April 28th to May 2nd, and from the 5th to the 6th. Barry was frustrated on the last day by Letts' insistence that he achieve the Robot's attack on the tank by having a foreground Action Man toy vanish via roll-back-and-mix -- an effect which proved highly unsuccessful. Barry had also reserved May 7th as a spare day in case his schedule was upset due to industrial action by the BBC's scene shifters, but this does not appear to have been utilised.

Recording was then intended to begin with a two-day session on Tuesday, May 21st and Wednesday the 22nd in BBC Television Centre Studio 3, covering all the material from the first two episodes. However, the scene shifters' labour dispute caused the cancellation of the first recording day, and limited the shots Barry could accomplish on the second. He ended up taping scenes set in the vault, the Thinktank workshop, and Kettlewell's lab on the 22nd -- although due to the strike, a stepladder which had been left on the latter set had to remain in place, forcing Barry to shoot around it. The industrial action also meant that the Doctor Who sets could not be struck after recording had wrapped, and the next day's episode of Blue Peter had to be taped on them as a result.

Fortunately, Letts was able to reschedule the entire studio session for Saturday, June 1st and Sunday the 2nd, again in TC3. Most of the scenes attempted on the 22nd were remounted; part one was recorded on the first day alongside the first five scenes of part two, while the rest of that installment was taped on the second day, in addition to the opening scene of part three. The concluding studio session then went ahead as scheduled, on Thursday the 6th (for the remainder of part three and episode four material set in the control room and the corridor) and Friday the 7th (for the outstanding segments of part four) in TC3. Letts and Barry became unhappy with some of the CSO sequences involving the Robot during editing, however. A remount was finally scheduled for October 24th in TC7, with Elisabeth Sladen and Michael Kilgarriff reprising some of the scenes featuring Sarah and the Robot.

The conclusion of work on Robot brought Doctor Who's eleventh recording block to an end, and saw Barry Letts earn his final credit as the programme's producer, although he continued to supervise Hinchcliffe for the first two serials of the next group of episodes. After leaving Doctor Who, Letts continued to produce and direct, with much of his work concentrating on classics serials for BBC1 (sometimes in concert with Dicks). These included an adaptation of Arthur Conan Doyle's The Hound Of The Baskervilles, starring Tom Baker as Sherlock Holmes. Letts would also return to Doctor Who as both a director (on The Android Invasion) and an executive producer (supervising novice producer John Nathan-Turner during Season Eighteen). In the Nineties, he scripted The Paradise Of Death and The Ghosts Of N-Space, two Doctor Who radio dramas starring Jon Pertwee. Letts later novelised these stories for Virgin Publishing. He also contributed two Third Doctor adventures to BBC Books' line of Doctor Who novels: Deadly Reunion (cowritten with Dicks) and Island Of Death.

Hinchcliffe, meanwhile, had decided to save money by avoiding a complete redesign of the Doctor Who title sequence and logo. These had just been revamped the year before, and so he instead asked Bernard Lodge to make only minor changes them, replacing Pertwee's profile with Baker's and incorporating an image of the TARDIS. This amended sequence heralded the start of Season Twelve and the Tom Baker era of Doctor Who on December 28th. The 8.4 million viewers who tuned in could scarcely have realised that they were witnessing the start of the transformation of Doctor Who from British television stalwart to worldwide cult phenomenon...

• Doctor Who: The Handbook: The Fourth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing, ISBN 0 426 20369 8.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing, ISBN 1 85227 444 1.
• Doctor Who Magazine #290, 3rd May 2000, “Archive: Robot” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #8, 1st September 2004, “You Ain't Seen Nothing Yet” by Andrew Pixley, Panini Publishing Ltd.
• In-Vision #1, January 1988, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.