On Gallifrey, the Doctors home planet, 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 known as the Renegade. 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 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, 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, another technician in the records section, the Doctor is soon taken for execution, despite Nyssa’s attempts to save him, and placed in a dispersal chamber. 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, 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, the Doctor’s former companion Tegan Jovanka arrives looking for her cousin Colin Frazer and 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 and 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, 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 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, 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 control of the Matrix and, therefore. Fortunately the Doctor and Nyssa manage to slip away and return to the TARDIS, 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 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
Image: Omega as Doctor
Omega's costume for this episode, on display at the Doctor Who Experience.