While on holiday at the Eye of Orion, the fifth Doctor rebuilds the main console of the TARDIS, perhaps using data on the Master’s ship stored within Kamelion’s databank, since the new console is identical to the one later seen in the Master’s TARDIS. After working out a few bugs, this console seems to finally give the Doctor the means to steer the ship properly, since he more and more arrives places intentionally rather than by chance.
The Doctor: Yes. Looks rather splendid, doesn’t it?
Tegan: But will the TARDIS work properly?
The Doctor: Of course, once everything’s running.
Tegan: Didn’t you repair anything?
The Doctor: Well, the TARDIS is more than a machine, Tegan. It’s like a person. It needs coaxing, persuading, encouraging.
Tegan: You mean it’s just as unreliable.
The Doctor: You have little faith, Tegan.
Tegan: Do you blame me?
The second Doctor turns up at UNIT headquarters to hear Brigadier Lethbridge-Stewart’s speech at the reunion celebration. They reminisce about yeti, Cybermen, Omega, and the Doctor mentions Zodin, though the Brigadier is oblivious.
The Doctor: And who is this?
The Brigadier: That’s Colonel Creighton, my replacement.
The Doctor: Mine was pretty unpromising, too.
Members of the High Council of the Time Lords including Lord President Borusa, Chancellor Flavia, and the Castellan bring the Master to Gallifrey to offer him a complete set of 12 regenerations, a new life-cycle, if he agrees to rescue the Doctor from the Death Zone, “the dark secret at the heart of the Time Lord’s paradise,” which has recently become reactivated. It is draining energy from the Eye of Harmony to such an extent so as to threaten all Gallifrey. When the Master asks if they want him because he is disposable, the Castellan says, “Not at all. You would be useless to us dead.”
The first Doctor and Susan escape from a Dalek only to discover they are not on Skaro, but have both been brought back to Gallifrey and deposited in the Death Zone. Sensing the answer lies in the Dark Tower, they set off to reach it, as do the second Doctor with the Brigadier and the third Doctor with Sarah Jane Smith. Crossing the Death Zone, the first Doctor and Susan find the TARDIS and the fifth Doctor, Tegan, and Turlough within. The fifth Doctor seems pleased to see Susan again. She seems some years older than when he left her on twenty-second century Earth to marry David Campbell. Since she has not regenerated yet, it is likely she is still Susan Campbell.
The second Doctor explains their predicament to the Brigadier.
The Doctor: It’s just as I feared. We’re on Gallifrey, in the Death Zone.
The Brigadier: You know this place?
The Doctor: To my shame. Yes, mine, Brigadier, and that of every other Time Lord. In the days before Rassilon, my ancestors had tremendous powers which they misused disgracefully. They set up this place, the Death Zone, and walled it around with an impenetrable force field. And then they kidnapped other beings and set them down here.
The Brigadier: But what for?
The Doctor: I’ll explain as we go.
The Brigadier: Where are we going?
The Doctor: To the tower -- to Rassilon, the greatest single figure in Time Lord history.
The Brigadier: Is that where he lives?
The Doctor: Not exactly, Brigadier. It’s his tomb.
* * *
The Doctor: I wonder. Could Rassilon himself have brought us here?
The Brigadier: Hang on a minute, Doctor. You said this chap Rassilon was dead. You did say that was his tomb.
The Doctor: Oh, it is. But no one really knows how extensive his powers were.
The Brigadier: He could still be alive?
The Doctor: Watching us at this very moment.
The Brigadier: Didn’t you say he was supposed to be rather a good type?
The Doctor: So the official history says. But there are many rumors and legends to the contrary. Some say his fellow Time Lords rebelled against his cruelty and locked him in the tower in eternal sleep!
Driving toward the Dark Tower in Bessie, the third Doctor and Sarah Jane encounter the Master.
The Doctor: Jehosaphat! It really is you. Yes, well, I should have known you’d be behind all this.
Sarah Jane: Doctor, who is it?
The Doctor: It’s my best enemy. He likes to be known as the Master. Don’t you? My, my, my, but you’ve changed. Another regeneration?
The Master: Not exactly.
The Doctor: I take it you are responsible for our being in the Death Zone.
The Master: For once, I’m innocent. Here at the High Council’s request to help you and your other selves.
The Doctor: You sent here by the Time Lords to help me? I’ve never heard such arrant nonsense.
After transmatting to the council chamber, the fifth Doctor mentions to the High Council that even in the ancient times, the Cybermen were prohibited from playing the Game of Rassilon because they played too well. A search of the Castellan’s quarters produces a box containing the Black Scrolls of Rassilon, which contain forbidden knowledge from the dark time. Attempting to escape, the Castellan is shot dead. The Doctor is certain, however, that the Castellan is innocent and was framed, and that the real traitor is still at large.
Trying to bypass the death traps within the tower, the first Doctor and Tegan run into the Master.
The Master: Our ancestors had such a wonderful sense of humor.
The Doctor: Do I know you, young man?
The Master: Believe it or not, we were at the academy together.
Tegan: What do you want?
The Master: To help.
After parting, the Doctor exclaims, “What an extraordinary fellow!” As the various parties near the Tomb of Rassilon, they encounter a psychic field that causes feelings of intense fear and anxiety. They also meet phantoms from the past who warn them away. When the second Doctor sees Jamie McCrimmon and Zoe Heriot, he recognizes them immediately. He seems to know what happened to them after his exile to earth, but how he could possibly know that is not explained. Bypassing the defenses, the first three Doctors reach the tomb, where they translate an ancient inscription on a small obelisk written in Old High Gallifreyan, the ancient language of the Time Lords. The inscription promises immortality to whomever puts on the ring from Rassilon’s finger.
Meanwhile, the fifth Doctor discovers the secret lair of the traitor, who turns out to be Borusa, Lord President of the High Council of the Time Lords. Borusa has decided he wants to rule Gallifrey for the rest of eternity, and found the answer in the legends of Rassilon, who left behind him coded instructions which Borusa believes he has solved. He wants the Doctor as his servant.
The Doctor: I will not serve you.
Borusa: You have no choice, Doctor. I wear the Coronet of Rassilon.
The Doctor: And very fetching it is, too.
Borusa: It emphasizes my will and allows me to control the minds of others.
Transmatting directly to the Tomb of Rassilon, Borusa activates an image of Rassilon which appears over Rassilon’s body and offers him immortality. As Borusa places the ring on his finger, his life force is absorbed into the tomb itself, granting him the worst kind of immortality imaginable, a fitting punishment for his greed. After congratulating the Doctor, the image of Rassilon fades.
The fifth Doctor: Did you know what would happen?
The first Doctor: I’m so sorry. I suddenly realised what the old proverb meant. “To lose is to win, and he who wins shall lose.” It was all part of Rassilon’s trap to find who wanted immortality and put him out of the way. He knew very well immortality was a curse, not a blessing.
The fifth Doctor: Well, now it seems we must part, just as I was getting to know me.
The second Doctor: So, you’re the latest model?
The fifth Doctor: Yes, and the most agreeable.
The second Doctor: Certainly the most impudent.
The third Doctor: And our dress sense hasn’t improved much, has it?
The first Doctor: Neither our manners. Well, good bye, my boy. You did quite well, quite well. It’s reassuring to know my future is in safe hands. Come along, Susan.
Susan: Good bye, everybody.
The fifth Doctor: Good bye.
The third Doctor: Good bye, Susan.
The second Doctor: Good bye. Time to go, Brigadier. Well, good bye.
The fifth Doctor: Good bye.
The second Doctor: Good bye, fancy pants.
The third Doctor: Scarecrow.
The Brigadier: Doctor, don’t you want your coat?
The second Doctor: Bring it along, would you, Brigadier?
The Brigadier: Certainly. Good bye, Doctor -- Doctors.
The third Doctor: Brigadier.
The Brigadier: Splendid fellows, all of you.
The third Doctor: Well, good bye, my dear chap. I must say, I’ve had the time of my lives. Haven’t we, Sarah Jane?
Sarah Jane: Have we? Well, I only have one life, and I think I’ve had too much already. Good bye. It was really nice meeting you.
The third Doctor: Thank you, Sarah Jane. It was nice meeting you, too.
Sarah Jane: What?
The third Doctor: I’ll explain later.
The fifth Doctor: I’m definitely not the man I was. Thank goodness.
Arriving with members of the guard, Chancellor Flavia informs the Doctor that the full council has exercised its emergency powers and appointed him Lord President. The Doctor grants her full deputy powers until he returns and then beats a hasty retreat into the TARDIS. Despite incurring the wrath of the Time Lords, the Doctor has no intention of being president of anything, and he, Tegan, and Turlough continue on their travels. The Doctor makes use of the title on occasion until he is eventually dismissed from office due to dereliction of duty. It is apparently Borusa who was behind the scheme to move the Earth across the galaxy to prevent the Andromedans from gaining the secrets of the Matrix, and presumably Flavia was running the High Council when they were all deposed following the revelation of this conspiracy. Nothing is known of the new Time Lord government formed following that scandal, only that revolt swept Gallifrey. It is also unknown what was done with the Tomb of Rassilon or the Time-Scoop after the resolution of Borusa’s final scheme. The Doctor insisted it would have to be sealed again, but he left everything in Flavia’s hands. It’s a little uncertain from what point in history each of the Doctors came from. It was evidently after “The Three Doctors” for the first three, and after the third Doctor met Sarah Jane. But the second Doctor displays some rather problematic knowledge, since he regenerated immediately after his trial.