Season ten of Doctor Who kicks off with the first anniversary special, in which the first two Doctors return to join the third in an adventure that reveals much about Time Lord history. Following this story, the Doctor’s exile is rescinded, and he is free to roam time and space once more. Then, the Master and the Daleks team up to menace the Doctor, in what would turn out to be Roger Delgado’s final appearance in the series.
From “The Three Doctors”
The Doctor is brought evidence of a superluminal energy beam directed at Earth, along which has traveled a strange matter / antimatter goo. When several monsters attack UNIT headquarters to get the Doctor, he and Jo Grant take refuge in the disabled TARDIS, forcing the Doctor to contact the Time Lords for help. Meanwhile, the Time Lords have discovered the energy beam originates from within a black hole that is quickly draining away all power from the Time Lords, disabling them.
Chancellor: Are you telling me we’re up against an adversary -- a force equal to our own?
President: Equal and opposite to our own!
Chancellor: A force which inhabits a universe where by definition even we cannot exist?
President: Yes, a force in the universe of antimatter!
Chancellor: But that’s too terrible to contemplate! Someone must go and help the Doctor!
President: I agree, but no one can be spared, Your Excellency. Everyone is needed to combat the energy drain.
Chancellor: Are you saying we can’t help him?
President: Yes, I am. But perhaps he can help himself. Show me the Doctor’s time stream, the section for his earlier self, before he changed his form.
Chancellor: You cannot allow him to cross his own time-stream! Apart from the enormous energy it would need, the First Law of Time expressly forbids him to meet his other selves!
President: I am aware of that, Your Excellency. But this is an emergency.
Chancellor: But you can’t!
President: Your Excellency, I have to!
Chancellor: Be it on your own head!
In the TARDIS, a recorder suddenly appears on the main console, which the Doctor says looks strangely familiar. Suddenly, his previous incarnation materializes, explaining that the Time Lords were able to lift him from his present and deposit him into his own future. The two Doctors begin squabbling immediately, so the Time Lords summon up his first incarnation to keep them in line, but he becomes trapped in a time eddy and can only appear on the TARDIS viewscreen. The goo transports the third Doctor and Jo to a planet within a singularity in the antimatter universe. As the second Doctor tries to fill in the incredulous Brigadier Lethhridge-Stewart, the goo becomes agitated again, causing them to retreat back into the TARDIS. It is the first time inside for both the Brigadier and Sergeant Benton. The second Doctor offers them some jellybabies. Meanwhile, the third Doctor learns the identity of his kidnapper -- Omega, the legendary Time Lord the Doctor thought dead.
Omega: Without me, there would be no time travel. You and our fellow Time Lords would still be locked in your own time, as puny as those creatures you now so graciously protect.
The Doctor: You knew your mission was dangerous.
Omega: Dangerous, yes. But I completed it! And I did not expect to be abandoned! Many thousands of years ago when I left our planet, all this was then a star, until I arranged its detonation!
The Doctor: You were the solar engineer. It was your duty.
Omega: It was an honour, or so I thought then. I was to be the one to find and create the power source that would give us mastery over time itself!
The Doctor: Well, you succeeded. And are revered for it.
Omega: Revered? Here? I was abandoned!
The Doctor: Histories say you were lost in the super-nova.
Omega: I was sacrificed to that super-nova! I generated those forces, and for what? To be blown out of existence into this black hole of antimatter? My brothers became Time Lords, but I was abandoned and forgotten!
The Doctor: No, not forgotten. All my life I’ve known of you and honoured you as our greatest hero!
Omega: A hero? I should have been a god!
Omega demonstrates that in the singularity, he can manipulate reality with his mind, which allowed him to survive and create the matter / antimatter goo that enables the Doctor, Jo, and the others to exist in the antimatter universe.
The Doctor: How do I fit into this picture?
Omega: There are some things that even I cannot do, not alone. And at this point in my plans, I need the help of a brother Time Lord.
The Doctor: Oh, I see.
Omega: And it pleases me to use you against them.
The goo then transports the whole of UNIT headquarters through the black hole, and the second Doctor is also brought before Omega, who deduces that they are both the same person. Omega intends for the Doctors to take over maintaining the energy beam so that he can escape, but the Doctors discover that Omega’s physical form has dissolved completely, and that he can now exist only within the singularity. The second Doctor finds his recorder had slipped into the TARDIS force-field generator, and is therefore still composed of matter. When Omega disrupts the field, the atoms annihilate each other, destroying the singularity and sending all the matter back to its point of origin. The black hole collapses and Omega is once again lost. The first two Doctors are returned to their respective points in the time stream, and the third Doctor receives a gift from the Time Lords.
The Doctor: The Time Lords -- they’ve sent me a new dematerialisation circuit! And my knowledge of time travel law and all the dematerialisation codes, they’ve all come back! They’ve forgiven me … they’ve given me back my freedom!
From “Carnival of Monsters”
Attempting to take Jo on a trip to Metebelis III, the Doctor finds the TARDIS has materialized instead on Inter Minor, within a device that contains miniaturized alien environments.
The Doctor: As a matter of fact, I had a great deal to do with the banning of these miniscopes.
Jo: You did?
The Doctor: Yes, I did. I managed to persuade the High Council of the Time Lords that they were an offence against the dignity of sentient life forms.
Jo: But I thought the Time Lords never interfered.
The Doctor: Well, they don’t as a rule. But frankly, I made such a nuisance of myself -- well, they banned the things.
Jo: But if these scope things were banned, how come we’re inside one?
The Doctor: I don’t know. Officially, they were all called in and destroyed.
From “Frontier in Space”
After leaving Inter Minor, the TARDIS nearly has a hyperspace collision with a 26th century space freighter, but manages to materialize on board just in time. The Doctor and Jo find themselves in the middle of a plot by the Master to start a war between the Earth and Draconian space empires. The Master is employing the Ogrons as his henchmen and turns out to be in league with the Daleks, who plan to invade the Milky Way galaxy in the aftermath of the war. Although he asked for only the Earth, the Master intended to double-cross the Daleks and seize total power for himself. The Doctor and Jo escape the Master’s clutches in the TARDIS, but not before the Doctor is wounded by the Master’s ray gun. The Doctor sends a telepathic message to the Time Lords, asking them to send the TARDIS after the Dalek task force. His scheme collapsing, the Master also escapes, not to encounter the Doctor again until their disastrous homecoming.
From “Planet of the Daleks”
The Doctor collapses and falls into a deep coma as a result of his injuries. When the TARDIS finally materializes, Jo goes out to look for help. The Doctor then comes round, only to find the TARDIS doors jammed and the oxygen supply depleted. He is rescued by a group of Thals from Skaro, on an interstellar expedition to the planet Spiridon. The Thals mention their ancient legend of the Doctor and his three companions who once helped them escape the Daleks. Now, a Dalek army has come to Spiridon to learn the secret of invisibility, having subjugated the natives by using germ warfare, and are marshaling their forces for the invasion of the Milky Way galaxy. However, the Doctor buries the Dalek army in an ice floe.
From “The Green Death”
At UNIT headquarters, Jo is having a quick breakfast while the Doctor tinkers with components from the TARDIS.
Jo: Is that the dematerialisation circuit?
The Doctor: No, no. No more trouble there, thank goodness. I can now take the TARDIS wherever and whenever I like. I’ve got absolute control over her.
Jo: Now the Time Lords have forgiven you.
The Doctor: Yes, exactly.
Jo: Well, what is it then?
The Doctor: What, this? This is the space-time co-ordinate programmer. The wretched thing’s nearly worn out. That’s the trouble with the TARDIS, she’s getting on a bit, you know, Jo.
The Doctor: Look, must you?
Jo: I’m sorry, it’s my breakfast. I said no wonder we never got to Metebelis III.
The Doctor: There’s precious little protein in an apple, you know. Protein’s the thing for breakfast, Jo.
Jo: Eggs and bacon? Yuck!
The Doctor: That’s where we’re going to next.
Jo: Where are we going?
The Doctor: Metebelis III. The TARDIS can’t miss this time. I’ll actually wire the coordinates into the programmer.
News of a mysterious death at Global Chemicals in Wales leads the Brigadier to ask the Doctor and Jo to assist the investigation. Jo intends to help a group led by Professor Clifford Jones, which opposes Global Chemicals. The Doctor, however, insists on going to Metebelis III, and the three of them go their separate ways. Metebelis III turns out to be a nightmarish experience, but the Doctor manages to pocket a blue crystal. He then joins the Brigadier in Wales, where they find a mine infested with giant maggots. As the UNIT troops arrive in force, the Doctor realizes that Jo is falling in love with Professor Jones. He also discovers that Global Chemicals is run by a sentient computer that has enslaved the human employees, and that the blue crystal can overcome the mental conditioning. The computer thus destroyed, Professor Jones and Jo announce their plans to be married and go on an expedition to the Amazon Jungle. The Doctor gives Jo the crystal from Metebelis III as a wedding gift.