Arc of Infinity
Arc of Infinity was the first story of the Doctor Who anniversary season 20. Janet Fielding returned as Tegan Jovanka in this serial, rejoining the Fifth Doctor and Nyssa on their travels. Future Doctor Colin Baker made his Who debut in this story, playing Commander Maxil. Just over a year later, he would take over as the Sixth Doctor at the end of season 21. Of the several Doctor Who stories filmed outside the UK in the late 1970s-early 1980s, this was the only one to open a season.
On Gallifrey, a Time Lord is at work stealing the biodata extract of another Time Lord and killing a technician who stumbles across the crime. The traitor provides the bio-data to a creature composed of anti-matter and uses the bio-data to invade the TARDIS and then the Fifth Doctor’s metabolism. The Doctor’s companion, Nyssa, helps him recover. The creature is shielded in this attempt by the Arc of Infinity, a curious curve between the dimensions containing quad radiation which can shield anti-matter. The Doctor decides to head to Gallifrey to track down the supplier of his bio-data, conscious that, unless the creature trying to cross universes is stopped, its incursion could cause a fatal chain reaction to our universe.
Meanwhile, in Amsterdam, Netherlands, backpackers Robin Stuart and Colin Frazer decide to crash at the crypt of the Frankendael mansion.
During the night, Colin hears something and investigates; he finds a curious birdlike creature, the Ergon, which hypnotizes him. A terrified Robin runs away.
The High Council of the Time Lords is also taking the matter seriously and has decreed that the Doctor’s TARDIS should be recalled. The Chancellery Guard under the over-zealous Commander Maxil seizes the Doctor and Nyssa. When the Doctor resists arrest, Maxil shoots him…
The Doctor has been stunned to ensure his delivery to the High Council. When he is brought before the High Council the new Lord President, Borusa, is inscrutable while Chancellor Thalia and Cardinal Zorac are openly hostile; only his old friend Councillor Hedin seems pleased to see him.
The President stresses the gravity of the situation since the creature poses such a threat to the Universe, and the High Council has had no alternative but to issue a Warrant of Termination on the Doctor to ensure the creature can no longer bond with him. Fortunately an old friend, Damon, who is another technician in the records section, provides him with the proof he needs that a member of the High Council stole his bio-data extract.
Meanwhile, the Doctor’s former companion, Tegan Jovanka, arrives in Amsterdam looking for her cousin Colin. Instead, she is greeted by Robin, who tells her that Colin has disappeared. When neither of them can persuade the police to take an interest they decide to investigate the crypt themselves.
The Doctor is soon taken for execution, despite Nyssa’s attempts to save him, and placed in a dispersal chamber. Sentence is carried out…
The supposed death of the Doctor, however, has not solved the situation. Unbeknownst to the High Council, his mind has been taken into the Time Lord living repository of knowledge, the Matrix, while his body is hidden behind a force shield in the termination cubicle. The creature is a renegade Time Lord, who demands an opportunity to return to the Universe it once inhabited. The truth of the aborted execution is discovered by the wily Castellan, who tells first Nyssa and Damon that the Doctor is alive, and then the High Council.
Tegan and Robin are attacked by the Ergon’s weapon, a matter conversion gun, and transported into a TARDIS hidden at the Frankendael and belonging to the renegade. Their minds are scanned, revealing to the creature that Tegan knows the Doctor. The renegade uses Tegan as bait to force the Doctor to obey him, also releasing Colin from his slavery as a reward. The Doctor is returned to normal space on Gallifrey where he makes for the High Council Chamber. Lord President Borusa has fallen under suspicion of being a traitor because the Castellan reveals it was his codes that were used to transmit the bio-data. The truth, however, is that Councillor Hedin is the traitor. He is in awe of his master – the mighty Omega, first of the Time Lords and pioneer of time travel.
Hedin wishes to release Omega from his exile in a universe of anti-matter, not realizing the great Time Lord has been driven mad by his years of solitary confinement. The Castellan kills Hedin, but this does not prevent Omega using the Arc of Infinity to seize total control of the Matrix and, therefore, the organisation of Gallifrey…
Fortunately the Doctor and Nyssa manage to slip away and return to the TARDIS. They use scant knowledge provided by Tegan to determine that Omega has established his base in Amsterdam on Earth, and head there immediately, desperately trying to find the Frankendael crypt she described. After a lengthy hunt they find the lair defended by the Ergon, and Nyssa disposes of it with its own matter-converter gun. They reach Omega’s TARDIS at the point at which both the ship is destroyed and Omega makes full transference to Earth using the Arc of Infinity. When he peels his decayed mask away he reveals the features of the Doctor.
Omega heads off into Amsterdam with the Doctor, Tegan and Nyssa in hot pursuit. Within a short time the Doctor’s prediction of an unstable transfer begins to come true: Omega’s flesh decays and it is clear his new body is not permanent. When the Doctor, Tegan and Nyssa catch up with him it is a painful task for the Doctor to use the Ergon’s anti-matter converter on Omega, expelling him back to his own universe of anti-matter. The Time Lord High Council on Gallifrey detects the end of the threat.
Once Tegan has checked on her cousin’s progress in hospital, she decides to rejoin the TARDIS crew. This time it is as a willing traveler.