This story was an inspiration of sorts for the Doctor Who episodes "Rise of the Cybermen"/"The Age of Steel" (on which Marc Platt got a story credit): one of the story's most powerful scenes (a partially-converted Cyberman doesn't understand what's been done to her) is drawn from this audio. The character of Yvonne Hartman, appearing in "Army Of Ghosts"/"Doomsday", is additionally a Composite Character of this story's Yvonne Hartley and Doctorman Allan.
This story would inspire another television two-parter story, eleven years later, "World Enough and Time"/"The Doctor Falls", dealing with the origins of a different set of Mondasian Cybermen in a similar way - the Doctor notes they're a parallel evolution of the race, just like on Mondas, Telos, Earth, Marinus and Planet 14. That episode takes some stylistic cues from this one, notably the pseudo-1950s setting.
Beyond that, it's considered an absolute classic Doctor Who story.
Earth's long-lost twin planet, Mondas, drifts through interstellar space, while the nearly extinct human population live in the last populated underground city. Resources are nearly gone, health is poor for just about everyone, and organ replacement — both organic and manufactured — is commonplace. Events are already spiraling towards a final end for Mondasian civilization, but the approaching Cherrybowl Nebula may rip Mondas apart unless they can activate the untested planetary propulsion system.
The Fifth Doctor and Nyssa land on Mondas. By the time the Doctor realises where and when they are, Nyssa has already befriended a sweet young woman named Yvonne Hartley and her family. The Doctor tells her that there is nothing they can do to save this planet, but Nyssa is still traumatised by the events of "Earthshock", and she decides to stay with the family during their final days. She also brings Yvonne's pet Cybermat into the TARDIS, which promptly starts chewing on wires, causing a fire. The Doctor has to really take a moment to step outside and regain his composure.
Yvonne is drafted into the surface crew and taken away from her dad and brother. Since the surface's atmosphere is impossible to stay alive in, she's given a prototype suit and (due to a power failure) only partially converted. Since organ failure is everywhere, people have started upgrading their entire bodies just to stay alive... and then lobotomising the sick to help cope with their constant pain and grief. This, combined with the prototype suits for surface exploration, resulted in the very first Cybermen, who were promptly judged more efficient than ordinary humans by the ruling Committee, who started trying to convert the rest of the population. The Doctor knows he shouldn't meddle, since You Can't Fight Fate, but his Adric-related Survivor Guilt causes him to investigate anyway, leading him to an unscrupulous organ dealer.
Both are soon captured by Doctorman Allan, the inventor of the Cyber-suits. And when she realises that the Doctor has a body far more advanced than that of a human, she uses him as the blueprint for all Cybermen, which can now be converted with a far greater efficiency and with better chances of survival thanks to Allan's understanding of his Time Lord brain structure. Allan realises that she's dooming her own planet, but she did what she had to do for her country, and now sees it as her duty to at least dull the emotional pain of it all with institutionalised lobotomies.
Horrified about his unwilling contribution to the creation of the Cyber-race Doctor gets really very shouty and decides to give the Laws of Time a wide berth. He poisons the techno-organic Mondas Central Commitee (the first Cyber-Planner) by mixing bottles of Allan's booze into its nutrient feed and teaches Allan how to undo the cyberconversion. As the Doctor and Nyssa eventually leave, she asks about the damage he has potentially done to his personal timeline, but the Doctor admits that Rubber-Band History sometimes ends up sorting these thing out. It turns out he is right; Mondas society soon starts to collapse in on itself, and Allan's attempt at restoring the population is overthrown.
- Ac CENT Upon The Wrong Syl LA Ble: In a throw-back to the original Tenth Planet Cyber-Men, the prototype Cyber-Men speak like this.
- Adult Fear: Your daughter gets drafted into the army. By the time you see her again, she's been lobotomised.
- All Issues Are Political Issues: It's well known that Terry Nation modeled the Daleks after the Nazis, not so well-known that Kit Pedler modeled the Cybermen after the Soviets. Spare Parts takes this allegory and runs with it, with a completely state-run world where a shadowy "committee" delegates allocation of resources with ruthless efficiency.
- All That Glitters
- Beneath the Mondas
- Big Brother Is Watching You
- Blatant Lies: The Doctor trying to convince Nyssa that Mondas is Earth.
- Body Horror/Medical Horror: Aside from this being the core of every Cybermen story, there's Mr. Hartley's user-maintainable artificial heart and Yvonne's deeply upsetting fate.
- Bold Explorer: The Mondasians selected as explorers are portrayed as this, even if it's only a pretty lie.
- Catchphrase: The phrase "We. Will. Survive." is used repeatedly by the Cybermen in general, particularly the Central Commitee and their Dragon, "Zheng". It manages to sum up the whole species' character and drive pretty effectively.
- Cold Equation: The government claims to be cyber-converting civilians (A Fate Worse Than Death) to explore the planet's surface. The sacrifice of a few is expected to save their world. Of course, the Committee has more long-range plans.
- Creepy Monotone: The committee.
- Cybernetics Eat Your Soul: The conversion process preserves almost nothing of the actual person.
- Darkness = Death: No one goes out after dark.
- Downer Ending: See Foregone Conclusion. It appears as though the Doctor has won the day. The Cyber Planner is dead, Zheng is dead, and Doctorman Allan is working on ways to reverse the process. The Doctor and Nyssa leave Mondas, wondering how things might have changed. Only Zheng isn't actually dead...Zheng: "Doctorman Allan, we will begin again."
- Dying Vocal Change: Zheng appears to be undergoing this after being blasted by the Central Committee, his sing-song voice slowing to a drawn-out crawl. Then he turns up at the end, very much alive.
- Early-Bird Cameo: The unseen Eric Krailford that the Hartleys mention is better known as Cyberman Krail in "The Tenth Planet".
- Emotions vs. Stoicism: The emotional Doctor argues for quality of life against the stoic Mondasians' resolve to survive regardless of the terrible cost.
- Fascists' Bed Time: It's inevitable in this kind of Dystopia.
- The 50s: Invoked.
- Foregone Conclusion: Invoked, as the Doctor spends much of the story wrestling with the conflict between established history (ie. Cybermen) and his own decent nature that's imploring him to help the Mondasians.
- Ghost Planet: Mondas is turning into one.
- Grandfather Clause: This being an origin story, some aspects of the concept are explored and played in different ways, for example the name Cyberman is explained by the fact that Mondas often affixes 'man' to the end of a job title, e.g. doctorman, sisterman, electriman.
- Have We Met Yet?: The Fifth Doctor meets the Mondasians as they're just becoming the Cybermen. The First Doctor encountered the Mondasian Cybermen after their conversion was complete and they were set to assault Earth, so Five knows exactly what to expect. Ot mostly, at least - it turns out the bits that result in the Cybermen's weakness to gold haven't been introduced yet.
- Hive Mind: The Committee, as they give up their individual minds to fuse into a single entity - the first Cyber-Planner.
- Incurable Cough of Death: Yvonne; suffering from a chronic lung complaint, she hasn't been able to replace them with cyborg organs, and can only make do with pills. Later, while she's unwittingly waiting for cyber-conversion, Sisterman Constant diagnoses her as an "acute consumptive" reveals that she'll probably be dead in a few weeks anyway.
- Inexplicable Cultural Ties: Mondas bears an unusually strong resemblance to Earth, even for a Doctor Who planet. It's close enough that the Doctor tries to pass off Mondas as Earth.
- The Load: The Committee, since in their quest to live forever, they've squandered Mondas' few resources and led to a complete social stagnation.
- The Thing Behind The Curtain: The Committee.
- Mechanical Horse: With shades of Hellish Horse. Brrr. Though the Doctor, kindhearted as he is, can only pity the poor animal.
- Mind Probe: The Doctor.
- Nice Job Breaking It, Hero!: As the Doctor goes around trying to help the people of Mondas and avert the creation of Cybermen, he gets captured and a medical examination of him provides information that helps solve critical problems in the Cyberman design.
- Noble Demon: Commander Zheng, who helps kill the Cyber Planner when he realises it's prioritising its own survival over the people of Mondas.
- Not Quite Dead: Commander Zheng.
- O.O.C. Is Serious Business: The Doctor does not cope well with seeing Cybermen so soon after Adric's death, and gets a whole, whole lot more shouty than usual. He also decides to Screw Destiny. It doesn't take, but he gives it a damn good try.
- Pre-Mortem One-Liner:"Sorry, Doctor. I just froze your assets."
- Prequel: To "The Tenth Planet" and every other Cyberman story in the original series.
- Retraux/Revisiting the Roots: These are the original Cybermen - they have the original singsong voiceboxes, have no aim beyond survival, and still have some small indications of individuality like names.
- Robo Speak: The Cyber-Planner.
- Screw Destiny: The Doctor decides to go against what he knows should happen to give the people of Mondas a chance at survival.
- Shout-Out: The alcohol is one to Brave New World.
- A Spot Of Tea
- Strapped to an Operating Table: The Doctor.
- The Swarm: Of Cybermats.
- Take Me To Your Cyber-Leader
- Tampering with Food and Drink: The Doctor pours copious amounts of wine into the feeding system of the Cyber-Planner.
- Title Drop
- Trojan Horse: Nyssa thinks that Cybermats are just cute little pet robots, and brings one into the TARDIS (with disastrous results).
- Weaksauce Weakness: Averted when the Doctor tries to use gold dust. The Cyberman just sort of stares at him.
- Well-Intentioned Extremist: the Committee and, in his last line of dialogue, Commander Zheng. They just wanted to keep their people alive...
- What Measure Is a Non-Human?: The Doctor considers Cybermen no longer human in any way that matters. The Mondasians don't agree and still view the Cybermen as such.
- Who Wants to Live Forever?: The Mondasians. The Mondasians want to live forever.
- Wrong Genre Savvy: See Weaksauce Weakness.
- You Can't Fight Fate: The Cybermen will still appear in later events despite what the Doctor did to them.
- You Mean X Mas: It's never actually named in story, but a form of midwinter holiday is around the corner, complete with festive tree and decorating with lanterns.