Season twelve of Doctor Who saw the introduction of Tom Baker in the lead role, who would prove to be the longest-serving and generally most popular Doctor, in a series of interconnected stories. It began on familiar ground with a contemporary UNIT story, then moved on to bring back the Daleks, the Cybermen, and the Sontarans, as the producers began to really mine the resources of the “Doctor Who universe” that had grown up over the preceding decade. The Doctor and Sarah Jane were also joined by a new companion, Harry Sullivan.
Following his regeneration, the discombobulated Doctor can think only of leaving in the TARDIS as soon as possible. After overcoming UNIT’s medical officer, Lieutenant Harry Sullivan, the Doctor is prevented from disappearing only by some fast talking by Sarah Jane Smith and Brigadier Lethbridge-Stewart. Once he recognizes them again, he is intrigued by reports of thefts of components for a top-secret weapon. After choosing a new set of clothes, the Doctor deduces that the crimes were committed by a large robot. Sarah Jane discovers just such a machine at Think Tank, a scientific consortium that turns out to be a cover for the reactionary Scientific Reform Society’s plot to take over the world. When the villains hole up in their underground bunker, the Doctor uses his sonic screwdriver to open the door. After the plot is foiled and the robot is destroyed, the Doctor, Sarah Jane, and an unwitting Harry depart in the TARDIS, leaving Bessie to be mothballed by the Brigadier.
Surgeon-Lieutenant Harry Sullivan was attached to UNIT from the Royal Navy as a medical officer and, when called upon to treat the regenerated Doctor, found himself on a roller-coaster of adventures, which he managed to take in his stride despite some bumbling when out of his depth. Once back on Earth, Harry decided to steer clear of the TARDIS, seeing the Doctor again only when he and Sarah Jane turned up at the Space Defence Station where UNIT was operating.
From “The Ark in Space”
The Doctor was planning a trip to the moon until Harry fumbled with the helmic regulator, taking them to an orbiting satellite 11,000 years in the future. While trying to deactivate an automatic guard, the Doctor’s scarf is singed, prompting him to remark that it was made for him by Madame Nostradamus, a “witty little knitter.” They discover the station was built in the 30th century and is now a vast cryogenic repository used to escape Earth’s devastation by solar flares. The station has been infested by the insectoid Wirrn, who want the Earth for themselves. The alien creatures are destroyed in the station’s transport ship. With the ship destroyed and the humans resuscitated, resettlement of the Earth depends on the station’s transmit system, which has developed a fault. The Doctor, Sarah Jane, and Harry transmit down to the Earth to correct the problem, leaving the TARDIS aboard the ark.
From “The Sontaran Experiment”
After a slightly spotty materialization, the Doctor sets about repairing the transmit receptors. Sarah Jane and Harry go for a walk and they are soon separated. They fall into the hands of some marooned astronauts from an Earth colony that pre-dates the space station. The astronauts were led into a trap by the Sontaran Field-Major Styre, whose intention is to conduct experiments on the humans in preparation for the seizing of the Earth for its strategic use in their never-ending war with the Rutans.
Harry: Doctor, I thought you were both dead!
The Doctor: Not me. Piece of the synestic locking mechanism from Nerva’s rocket. Popped it in my pocket.
The Doctor: Foresight. You never know when these bits and pieces will come in handy. Never throw anything away, Harry. Where’s my 500-year diary? I remember jotting some notes on the Sontarans. It’s a mistake to clutter one’s pockets, Harry.
Harry: Yes, Doctor.
The Doctor challenges Styre to single combat in order to tire him out, forcing him to return to his sabotaged ship to re-energize. Styre is killed and the ship explodes. The Doctor uses Styre’s remote communication gear to turn back the Sontaran fleet. With the space station personnel ready to disembark, the Doctor, Sarah Jane, and Harry enter the transmit beam and dematerialize.
From “Genesis of the Daleks.”
The Doctor finds himself not aboard Space Station Nerva, but in a desolate landscape.
Time Lord: Ah. Welcome, Doctor.
The Doctor: What’s going on? Don’t you realise how dangerous it is to intercept a transmat beam?
Time Lord: Oh, come now, Doctor, not with our techniques. We Time Lords transcended such simple mechanical devices when the universe was less than half its present size.
The Doctor: Look, whatever I’ve done for you in the past, I’ve more than made up for. I will not tolerate this continual interference in my life!
Time Lord: Continual? We pride ourselves we seldom interfere in the affairs of others.
The Doctor: Except mine!
Time Lord: You, Doctor, are a special case. You enjoy the freedom we allow you. In return, occasionally -- not continually -- we ask you to do something for us.
The Doctor: I won’t do it. Whatever it is, I refuse!
Time Lord: Daleks!
The Doctor: Daleks? Tell me more.
Time Lord: We foresee a time when they will have destroyed all other life-forms and become the dominant creature in the universe.
The Doctor: That’s possible. Tell on.
Time Lord: We’d like to return you to Skaro at a point in time before the Daleks evolved.
The Doctor: Do you mean avert their creation?
Time Lord: Or affect their genetic development so they evolve into less aggressive creatures.
The Doctor: That’s feasible.
Time Lord: Alternatively, if you learn enough about their very beginnings, you might discover some inherent weakness.
The Doctor: All right. Just one more time.
Time Lord: You’ll do it?
The Doctor: Yes. If you’ll let me have the space-time co-ordinates, I’ll set the TARDIS for Skaro.
Time Lord: There’s no need for that, Doctor. You’re here. This is Skaro.
The Doctor: What?
Time Lord: We thought it would save time if we assumed your agreement.
The Doctor: What’s this?
Time Lord: A time ring. It will return you to the TARDIS when you’ve finished here. There’s just one thing.
The Doctor: What’s that?
Time Lord: Be careful not to lose it. That time ring is your lifeline. Good luck, Doctor.
The Doctor, Sarah Jane, and Harry find themselves caught up in a thousand-year war between the Kaled and the Thal peoples. The Doctor soon meets Davros, chief scientist of the Kaled people and creator of the Daleks. Davros provides the Thals with the capacity to annihilate the Kaled race before unleashing his new Dalek army on the Thals. The last surviving Kaleds are exterminated when the Daleks turn on their creator and declare their independence. The Doctor and the Thal survivors manage to entomb the Daleks in an underground bunker after destroying the incubator room. Davros is hit by a Dalek death ray, but the life-support system in his chair probably saves him from death. Feeling his mission sufficiently accomplished, the Doctor activates the time ring and he, Sarah Jane, and Harry depart from Skaro.
From “Revenge of the Cybermen”
The time ring brings the Doctor, Sarah Jane, and Harry back to Space Station Nerva, but the TARDIS is conspicuously absent.
The Doctor: Well, it probably hasn’t arrived yet. We’re a little early.
Harry: Hasn’t arrived yet?
The Doctor: No, you see, the TARDIS is drifting back through time, Harry. We’ll just have to wait for it to turn up.
The travelers have arrived thousands of years before Earth’s evacuation, when the space station is used as a beacon warning ships of a moon newly captured by Jupiter’s gravity. The moon is Voga, the planet of gold, and Nerva has fallen into the middle of a war between the Vogans and the Cybermen. The Doctor is able to turn the Cybermen’s weapons against them and they are destroyed aboard their ship. The TARDIS finally materializes and, while setting the drift compensators, the Doctor finds he has been summoned back to 20th century Earth by Brigadier Lethbridge-Stewart.