Series 20: Arc of Infinity

On Gallifrey a Time Lord traitor is at work stealing the bio-data code of another Time Lord and killing a technician who stumbles across the crime. The traitor provides the bio-data to a creature known as the Renegade, which is composed of anti-matter and uses the bio-data to invade the TARDIS and then the Doctor's metabolism. His companion, Nyssa, helps him recover. The Renegade 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 that its incursion could cause a fatal chain reaction to our universe.

The High Council of the Time Lords is also taking the matter seriously and has decreed that the Doctor’s TARDIS should be recalled for the same reason. The Chancellery Guard under the over-zealous Commander Maxil seizes the Doctor and Nyssa. He stuns the Doctor to ensure his delivery to the High Council. When the Doctor 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 Renegade 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 Renegade can no longer bond with him. The Doctor is taken away protesting, sure his bio-data has been compromised and stolen from within the High Council. 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 did indeed steal his bio-data extract. 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 Renegade, who demands an opportunity to return to the Universe it once inhabited, contacts him. 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.

Meanwhile in Amsterdam, Netherlands the Doctor’s former companion Tegan Jovanka arrives looking for her cousin Colin Frazer. She is greeted by his friend Robin Stuart who explains that Colin has disappeared while they were crashing in the crypt of the Frankendael mansion. When neither of them can persuade the police to take an interest they decide to investigate the crypt themselves. They find a hypnotised Colin working for a curious birdlike creature which is armed with a deadly weapon. They are rendered unconscious and their minds scanned, revealing to the Renegade, who has established its base in a TARDIS hidden at the Frankendael, 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 Time Lord in league with the Renegade. He is in awe of his master - the mighty Omega, first of the Time Lords and pioneer of time travel (see The Three Doctors). Hedin wishes to release Omega from his exile in a universe of anti-matter, not realising 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 its 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 birdlike creature, 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 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 his clear his new body is not permanent. When the Doctor 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 as a willing traveler.

Cast
Doctor Peter Davison (Fifth Doctor)
Companions Sarah Sutton (Nyssa)
Janet Fielding (Tegan Jovanka)
Guest stars
Leonard Sachs — President Borusa
Elspet Gray — Chancellor Thalia
Michael Gough — Councillor Hedin
Paul Jerricho — The Castellan
Max Harvey — Cardinal Zorac
Colin Baker — Commander Maxil
Ian Collier — Omega/The Renegade
Neil Daglish — Damon
John D. Collins — Talor
Alastair Cumming — Colin Frazer
Andrew Boxer — Robin Stuart
Maya Woolfe, Guy Groen — Hostel Receptionists
Malcolm Harvey — The Ergon

Production
Writer Johnny Byrne
Director Ron Jones
Script editor Eric Saward
Producer John Nathan-Turner
Executive producer(s) None
Production code 6E
Series Season 20
Length 4 episodes, 25 minutes each
Originally broadcast January 3–January 12, 1983

source: wikipedia