On Gallifrey, the Doctor's bio-data extract is stolen from the Matrix while, in Amsterdam, Tegan Jovanka's cousin goes missing after an encounter with something alien. When a being from an anti-matter universe begins to genetically bond with the Doctor, the TARDIS is summoned back to Gallifrey. There, the High Council orders the Doctor's execution, as a means of preventing the anti-matter entity from usurping the Matrix. Suspecting a traitor amongst the High Council, it falls to Nyssa to save her friend... while, on Earth, Tegan becomes enmeshed in the cosmic web of revenge which connects all of these events.

Shortly before he became Doctor Who's script editor in April 1981, Eric Saward watched the transmission of Johnny Byrne's The Keeper Of Traken, which he greatly admired. Unaware of the substantial rewrites carried out by former script editor Christopher H Bidmead, Saward contacted Byrne on September 30th with an invitation to submit ideas for Doctor Who's twentieth season. It was thought that he might contribute the year's opening serial, which meant that his storyline would have to address some very specific requirements.

First, producer John Nathan-Turner wanted to take Doctor Who overseas for just the second time in its history. In 1979, while still a production unit manager, he had been instrumental in arranging for City Of Death to be filmed on location in Paris, France. Nathan-Turner felt that Amsterdam would be a similarly affordable venue, especially since it was already used by the BBC on a regular basis for the soap opera Triangle. In order to justify the trip, Byrne was asked to make the Dutch city a key aspect of his storyline.

It would be Johnny Byrne's responsibility to reunite Tegan with the Doctor and Nyssa

Second, Byrne had to resolve the ending of the Season Nineteen finale, Time-Flight, in which Tegan had been inadvertently left behind on Earth. This cliffhanger had been designed to maintain viewer interest during the nine-month break between seasons, but no specific resolution had been planned. As a result, it would be Byrne's responsibility to find a way to reunite Tegan with the Doctor and Nyssa. To prolong the suspense, the writer was told to defer Tegan's reintroduction until the second episode.

When he was approached by Saward, Byrne was already toying with an idea in which an alien used a bridge between dimensions called the Arc Of Infinity to induce time shifts in London. Byrne felt that this concept could be relocated to Amsterdam, and it was suggested that a vacationing Tegan might stumble upon some form of criminal activity which would require the Doctor's attention. The production team stipulated that this should not involve drug smuggling, the theft of diamonds or Old Dutch Masters, or anything political.

On December 15th, Byrne submitted a storyline entitled “The Time Of Neman”. It involved the Doctor suffering nightmares about his regeneration, which were actually precursors to the arrival in his universe of an entity called the Avatar, who took on the Doctor's form and travelled to Amsterdam. Operating there as Neman -- a name recycled from The Keeper Of Traken -- the Avatar began to take control of human minds, striving to create a form in which it would be able to permanently maintain its existence. The Doctor and Nyssa discovered Neman's plot when they landed in a future version of Amsterdam, which was populated by robot guards called Sweepers, the elderly Resisters, and barbaric Anarchs. Realising that history had been altered, they travelled back in time to present-day Amsterdam. There they met Tegan, who had mistaken the Avatar for the Doctor. The Doctor discovered that Time Lord regeneration was the mechanism by which the Avatar was made manifest, and defeated his opponent by reliving his own recent regeneration.

Nathan-Turner and Saward had immediate concerns about “The Time Of Neman”, most notably the fact that the Amsterdam location was essentially incidental to the plot. It was also felt that the importance of the Doctor's dreams too closely resembled elements of Christopher Bailey's Snakedance, which was intended to follow “The Time Of Neman” in the broadcast order. Furthermore, following the success of the Master's return in The Keeper Of Traken, Nathan-Turner wanted his season premiere to bring back another old enemy. Amongst several returning villains nominated as possible replacements for the Avatar, Byrne reluctantly selected Omega, a renegade Time Lord who had last appeared in 1972's The Three Doctors. His inclusion was proposed by the Doctor Who production office's unofficial fan adviser, Ian Levine. Saward was pleased with the choice, because he wanted to revisit Gallifrey during Season Twenty.

To pave the way for Nyssa's departure, Johnny Byrne was asked to write her as being more mature

Now called “The Time Of Omega”, Byrne's scripts were commissioned on January 13th, 1982. As work on them proceeded, it was decided that Sarah Sutton would leave Doctor Who partway through Season Twenty. To pave the way for Nyssa's departure, Byrne was asked to write her as being more mature than previously depicted. Having created the character for The Keeper Of Traken, Byrne was glad to have the opportunity to develop Nyssa further. Meanwhile, additional references to the past were inserted into the scripts when the Lord President, originally unnamed, was identified as Borusa, who had last been seen as a Cardinal in 1978's The Invasion Of Time. Amongst the rest of the High Council, Cardinal Zorac was originally called Zoral.

Increasingly aware of Doctor Who fandom, Nathan-Turner decided that he wanted Omega's return to be a surprise for them and so, around the end of February, the title of Byrne's adventure became Arc Of Infinity. The scripts began to arrive around this time and, unfortunately, the production team was still dissatisfied with Byrne's justification of the Amsterdam setting. Although the writer had included elements such as a fusion booster which only functioned below sea level, it was felt that the location remained largely irrelevant. No obvious solution to this problem presented itself, however, and so no significant adjustments were made to Byrne's scripts.

Although Arc Of Infinity was planned as the first story of Season Twenty, it would follow Snakedance into production, so that the Amsterdam shoot would take place in the warmer May weather. Ron Jones was assigned to direct; he had last worked on Time-Flight. As pre-production progressed, Nathan-Turner encouraged costume designer Dee Robson to deviate from Omega's physical appearance in The Three Doctors. He thought that this would further help preserve the surprise of the villain's identity, and could be justified by Omega's nigh-total control over mass and form in his anti-matter domain.

Amongst the guest artistes cast by Jones in Arc Of Infinity was Colin Baker, playing Maxil. Baker had been suggested to Jones by assistant floor manager Lynn Richards, on the basis of his role in the Blake's 7 episode City At The Edge Of The World. Although eager to appear in Doctor Who, Baker was disappointed that his involvement in Arc Of Infinity would preclude him from ever portraying the Doctor himself. Ironically, just over a year later, Baker would find himself offered the role of the Sixth Doctor...

Location filming in Amsterdam began on May 3rd, with the first scenes completed at Schiphol Airport itself. Later the same day, Colin used a telephone box near the Munttoren, while the time travellers chased Omega through a nearby flower market. It was immediately evident that crowd control would be a major issue, as Dutch viewers recognised Peter Davison from his role as Tristan Farnon in All Creatures Great And Small. Nathan-Turner tried to assist Jones in dealing with the onlookers and, at one point, found himself attacked by an elderly woman who assumed he was a robber.

On May 4th, the characters could be seen traversing various parts of Amsterdam. This material included several elements for the climactic chase, which Jones had largely composed on his own while reconnoitring possible locations. Also recorded on this day was Robin taking refuge at Bob's Youth Hostel, Tegan and Robin at the police station along the Lijnbaansgracht, and the Doctor and Nyssa leaving the Vondelpark Youth Hostel. The scene where the Doctor and Nyssa consulted a telephone directory was taped near the Hoopman Bodega; in the transmitted version, Nathan-Turner could be seen in the background, shooing away a group of gawkers.

More of the chase sequence was filmed on May 5th, while the seventeenth-century Huize Frankendael became the property where Robin and Colin made their fateful decision to sleep rough. The latter part of the pursuit was recorded on the 6th around the Amstelsluizen lock. After supper that night, several members of the cast and crew decided to take a walk around Amsterdam. Unfamiliar with the city, they inadvertently ventured into its infamous red light district... where Janet Fielding found herself mistaken for a prostitute. The final shots required for the chase were then completed on May 7th, together with Tegan rejoining the TARDIS crew at the Blauburgwal Centraal train station.

Back in White City, London, studio work for Arc Of Infinity took place at BBC Television Centre Studio 1, starting with a two-day session on May 17th and 18th. In addition to material in the cafe (originally intended for the location shoot) and the youth hostel, the first day concentrated on scenes in the TARDIS corridors and console room. Baker found that his plumed headpiece -- which he'd nicknamed “Esmerelda” -- was too tall to accommodate his entrance through the TARDIS doors, and instead decided to carry it for the majority of his screen time. The second day dealt with sequences in Nyssa's room, as well as the Amsterdam crypt and its adjoining passages. The Ergon costume debuted on this day; its construction had been contracted out to props makers Imagineering of Witney, Oxfordshire. The Ergon was envisaged as an assemblage of bones, inspired by the eponymous creature in the 1979 film Alien. Sadly, this effect -- and especially the inclusion of a pterodactyl skull, which actor Malcolm Harvey wore as a hat -- did not come off as intended. With no time available to modify or replace it, the costume was judged a failure.

The servos which moved the flaps covering Omega's mouth were so loud that they could not be used

The second studio block was three days in length, running from May 31st to June 2nd. The first day saw Jones record scenes in Hedin's office, the Matrix and Omega's TARDIS. Although Richard Gregory of Imagineering was so happy with the Omega design that he wove his initials into the design on the chestplate, this costume also proved problematic. Imagineering had incorporated servos to move the flaps covering Omega's mouth, but these proved to be so loud that they could not be used.

Sequences in Omega's TARDIS were completed on the second day, alongside those in the computer room, the rest area, the security compound and the corridors. Finally, the last day was largely concerned with material set on Gallifrey: in the Council chamber, the termination area, and the offices of the Castellan and another Time Lord. An insert of the explosion in the pump house was also taped. With Arc Of Infinity complete, production of Doctor Who then paused for almost three months, while Davison recorded the third and final season of his sitcom Sink Or Swim.

As with Season Nineteen, Season Twenty would see two episodes aired each week. But whereas Doctor Who had been positioned on Mondays and Tuesdays in 1982, it would now be shifted to Tuesdays and Wednesdays. The exception was Arc Of Infinity Episode One, which instead aired on Monday, January 3rd while the Tuesday timeslot was reserved for the finale of Junior Kick Start. The programme's first Wednesday broadcast came at 6.45pm on the 5th, between the news and the John Wayne film Brannigan; Doctor Who was replacing the game show Top Secret in the BBC schedule. Its Tuesday timeslot, beginning on January 11th, was at 6.50pm, where Doctor Who was preceded by the news and followed by the American sitcom Best Of The West. For a second year running, it was replacing Angels on Tuesday evenings. Finally, Episode Four on the 12th saw Doctor Who lead into its regular schedule-mate, A Question Of Sport.

• Doctor Who Magazine #261, 11th February 1998, “Archive: Arc Of Infinity” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #1, 2001, “Diamond Life” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #36, 2017, “Story 123: Arc Of Infinity”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Eighties by David J Howe, Mark Stammers and Stephen James Walker (1996), Virgin Publishing.
• Doctor Who: The Handbook: The Fifth Doctor by David J Howe and Stephen James Walker (1995), Virgin Publishing.
• In·Vision #63, March 1996, “Production” edited by Anthony Brown, Cybermark Services.