Classic Who S20 • Serial 1 · (4 episodes)
Arc of Infinity
Omega, an ancient Time Lord made of pure anti-matter, once defeated by the Doctor, is plotting to cross over into this dimension by bonding with the Doctor. Meanwhile, the disappearance of a man in Amsterdam piques the curiosity of his cousin, Tegan, who previously left the Doctor at Heathrow Airport and now finds herself at Omega's mercy. Fearing total destruction from the collision of matter and antimatter, the Time Lords recall the Doctor to Gallifrey to undertake the only viable solution: executing him!
4 Episodes:
On Gallifrey, someone on the high council is perpetrating a treasonous act - transmitting the Doctor's bio-extract from the space/time matrix to an anti-matter being. On Earth, two English lads spend their last night in Amsterdam sleeping in a crypt where they're attacked by an alien creature under the same anti-matter being's control.
With an anti-matter being trying to enter the universe through the Doctor, risking the destruction of everything, there is only one clear course of action for the High Council of Time Lords to take: execute the Doctor. Meanwhile, Tegan arrives in Amsterdam and hears about what's become of her cousin from his unscathed friend.
Something seemed amiss about the Doctor's execution, so the Castellan has Commander Maxil discreetly but fully look it. Meanwhile, as the Doctor meets the anti-matter being inside the Time Lord Matrix, Tegan and her cousin's friend run afoul of a bird-like alien back on Earth.
The High Council creates a distraction so the Doctor and Nyssa can find Omega on Earth and prevent his reentry into our universe.