The Doctor, Jamie and Victoria land on Earth in the near future, where they are rescued from an attack by a woman named Astrid. She explains that the Doctor strongly resembles Salamander, a scientist who has developed a network of Sun-Catcher satellites intended to ease global hunger. But some believe that Salamander's real goal is global domination, and Astrid asks the Doctor to masquerade as his doppelganger to uncover the truth. The time travellers must navigate treachery and murder to uncover Salamander's true schemes, which are more devious than anyone suspects.

Shortly after completing the Season Four finale, The Evil Of The Daleks, David Whitaker was asked to contribute a new set of scripts for Doctor Who's fifth season. The Enemy Of The World was commissioned on July 25th, 1967. A key ingredient of this story would be the introduction of the Doctor's evil double, Salamander; the same plot hook had been employed for William Hartnell's Doctor in The Massacre Of St Bartholomew's Eve two years earlier. Although Patrick Troughton was disappointed that the plot required Salamander to be visually similar to the Doctor -- rather than allowing him to substantially modify his regular appearance -- he was still glad to have the opportunity to engage in the kind of dressing-up he enjoyed so much.

The director assigned to The Enemy Of The World was Barry Letts. This would be his first work on Doctor Who, although he had submitted story ideas which had been rejected by former story editor Gerry Davis in late 1966. Letts worked closely with assistant story editor Derrick Sherwin on The Enemy Of The World, as the scripts generally ran short and were felt to contain too much dialogue and too little action. In particular, it was Letts who suggested the opening chase sequence featuring a helicopter and a hovercraft, replacing logistically-difficult scenes set at a crowded holiday resort. The names of two of the hovercraft crew were changed from Tibor and Otto to Rod and Curly, respectively -- possibly suggesting that the setting was originally an Eastern European locale, rather than Australia.

Barry Letts agreed to restructure the final two installments to make Astrid more prominent

In the role of Astrid, Letts cast South African actress Mary Peach, who had starred in Inside Story and, more recently, The Three Musketeers. Shortly before production began, Letts was informed that Peach was backing out, having become unhappy that her character effectively disappeared from the narrative after Episode Four. Letts was eager to keep Peach on Doctor Who, and agreed to restructure the final two installments to make Astrid more prominent. Around the same time, on October 25th, Frazer Hines' contract to play Jamie was extended to include The Enemy Of The World.

On November 5th, production began with four days at Climping Beach in Climping, West Sussex, which posed as the shoreline where the TARDIS materialised. The Episode Five scene where Astrid was pursued across a field by a guard was also taped there. November 9th saw cast and crew travel to Ealing, London, where the exterior of Villiers House was used as Giles Kent's office, and Walpole Park was the site of the covert meeting between Jamie, Victoria and Astrid. Filming at the BBC Television Film Studios in Ealing then took place on November 10th, 11th and 13th. The middle day was used for model shots; otherwise, the main concern was the climactic TARDIS scene, which was the only one to feature the Doctor and Salamander together. Unfortunately, Letts was misinformed as to the best way to record these sequences, and the error was compounded by an equipment problem. This sorely limited the number of shots Letts could use in the finished programme.

As usual, each episode of The Enemy Of The World was recorded on successive Saturdays at Lime Grove Studio D in Shepherd's Bush, London. Episode One went before the cameras on December 2nd, and marked the first use of higher-definition 625-line videotape in Doctor Who, as opposed to the old 405-line standard. The following two weeks saw Frazer Hines' cousin, Ian Hines, join the cast as a guard. Neither Jamie nor Victoria appeared in Episode Four, and so both Frazer Hines and Deborah Watling were absent from the studio on December 23rd. On this day, Letts' nephew, Andrew Staines, was a last-minute replacement for another actor as the sergeant to Benik. During the next two weeks, it was Troughton's turn to see a family member play one of the guards, as his son, David, made his first appearance in Doctor Who. Recording for the serial concluded on January 6th, 1968.

Early in the New Year, the BBC Saturday schedule underwent a modification. For several weeks, Doctor Who had been followed by a news update, the chat show Dee Time and then the musical sitcom The Monkees. As of January 13th, the day that Episode Four of The Enemy Of The World was broadcast, Dee Time and The Monkees were interchanged.

The Enemy Of The World was the focal point of a series of changes in Doctor Who's key production roles. Most significantly, this would be the final story overseen by producer Innes Lloyd, who had wanted to leave Doctor Who for several months. As had been planned for some time, story editor Peter Bryant was pegged as Lloyd's successor. It was agreed that Derrick Sherwin would take over as story editor, which meant that a new assistant would have to be recruited as well. Sherwin himself only planned to remain on Doctor Who for a brief period of time, and so his intent was to hire someone whom he could quickly train as his own replacement. He therefore offered the post to his friend, Terrance Dicks, who joined the production team around the start of 1968.

Barry Letts remarked that Doctor Who should be scaled back to 26 episodes a year

It was also around this time that Troughton agreed to return to Doctor Who for a third season. At the same time, however, he confessed to Letts that he was becoming fatigued by the programme's gruelling pace of production. Troughton particularly disliked the fact that he, Hines and Watling were often required to film inserts for a serial on their days off, or in the midst of studio rehearsals for another story. Letts remarked that Doctor Who should be scaled back to twenty-six episodes a year -- compared to the forty-six episodes which would comprise the current recording block -- since this would permit a week's break between serials to deal with matters like pre-filming. Troughton was keen on the idea and suggested it to Bryant, who sought to implement it for the sixth production block, which would begin in late summer.

In addition to the departure of Lloyd, The Enemy Of The World was also the last story overseen by BBC Head of Drama Sydney Newman, the man who had spearheaded the development of Doctor Who in 1963. His contract having come to an end, Newman left the BBC to work for the Associated British Picture Corporation. However, his new employers were soon bought out, which prompted Newman to return to his native Canada. There he was a consultant to various bodies in the film and television industry, and was the chief commissioner of the National Film Board of Canada. Newman eventually returned to England; in 1986, he met with the BBC to discuss revamping Doctor Who, although nothing would come of this. Retiring to Canada, Newman died of a heart attack in Toronto, Ontario on October 30th, 1997.

• Doctor Who Magazine #219, 23rd November 1994, “Archive: The Enemy Of The World” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #4, 4th June 2003, “Heroes And Villains” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #11, 2016, “Story 40: The Enemy Of The World”, 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.