Written by Eric Saward. This four-episode serial first aired from March 8—16, 1982.
Lieutenant Scott and his squad of troops climb up a bleak hillside on Earth, escorting Professor Kyle, who had been part of a scientific expedition investigating the caves for fossil remains, to a camp set up by Scott's team. They find that Kyle's fellow paleontologists have gone missing. They're also followed by two shadowy figures.
Meanwhile, in the TARDIS, the Doctor and Adric are having a rather childish argument. Adric feels that he's being bullied, ignored and treated like an incompetent underling, and wants to go back home to E-Space. But the Doctor thinks it's too dangerous as E-Space is... E-Space. Either way, the Doctor materializes the TARDIS on 26th century Earth in a cave system and goes out for a little sulk. Nyssa and Tegan join him, pointing out dinosaur fossils in the walls as they go. (As they discuss the fossil, we even hear the first xylophone riff from the "Fossils" movement of Saint-Saens' Carnival of the Animals.) The Doctor mentions that he's always wanted to know how those dinosaurs died out.
Back with the missing-palaeontologists plot: the troopers decide to split up into multiple groups after suffering injuries exploring the cave system. They even pick up a few life signs — one of them with two heartbeats. The leader of this group reports his find to Scott, while his friend goes to help the wounded and like them is, sadly, turned into sludge. The survivors, led by Scott, stumble across the Doctor and the TARDIS and immediately notice that the Doctor, Tegan and Nyssa make great suspects. Before either group can make their case, however, those shadowy figures attack: Androids! Androids commanded elsewhere in a distant location by... the Cybermen!
Adric wanders out of the TARDIS and is nearly killed by one of the two Androids attacking everyone else, giving them a chance to take the Android out. The second one falls soon after, but the Doctor realizes that those who controlled the Androids were sending some sort of transmission to a hatch built into the cave. Opening the hatch, the Doctor is shocked to find a bomb has been set by whomever started this mess. The Doctor fiddles around with the bomb in an attempt to deactivate it, but actually activates the bomb with his fumblings and it takes the combined efforts of the Doctor and Adric together to turn the bomb back off again.
The Cybermen, for their part, realise that the Doctor is involved after seeing the TARDIS while reviewing the recorded images transmitted by the androids. They start preparing for his inevitable meddling as well, but not before the Cyber-Leader decides to show the audience some footage of the First, Second and Fourth Doctors from some of their Cybermen-oriented adventures.
The Doctor, satisfied with his deeds in the cave, ushers Adric, Nyssa and Tegan (as well as a few surviving humans from the cave) into the TARDIS. He decides to go trace the signal sent by the Cybermen to the Androids and the TARDIS materializes upon a freighter ship out in space that's suffered many random murders aboard during their travels to Earth. Almost immediately after stepping out of the TARDIS, the Doctor and Adric stumble across two dead bodies. Of course, the crew finds the Doctor and Adric standing over the bodies and blames them for the murders.
The Cyber-Leader chooses now to take over the freighter, and activates a unit of Cybermen. They hatch from their tombs and begin to stomp all over the ship as the Doctor and Adric are taken to the Captain, a middle-aged woman named Briggs who has the rare talent of sounding eternally drunk. The security chief decides to conveniently declare he's a double-agent for the Cybermen. The Doctor and Briggs barricade the bridge by shutting the doors and Captain Briggs at first seems confident that they can survive to Earth... until she realizes that there must be around 15,000 Cybermen on the ship, hiding in her ship's cargo.
Meanwhile, the people stuck in the TARDIS decide to go see what happened to the Doctor and Adric, only to find a few Cybermen running around. Tired of waiting around, Tegan joins them and shows she Took a Level in Badass somewhere along the line when she kills a Cyberman with its own gun. Back on the bridge, the Cybermen nearly break through by melting one of the doors... until the Doctor manages to re-solidify said door around a lone Cyberman. Of course, the Cybermen just blow up the other door and take the bridge anyhow. Bragging, the Cyber-Leader activates all the remaining Cybermen on the ship, proudly announcing how he's won the day — but not before killing off the security chief under the mistaken belief that he attempted to hide the existence of Scott and his troopers, proving that bad communication really does kill.
Finally, the Cyber-Leader announces his plan, which is so vast that it requires about 15,000 Cyber units. There is a massive meeting of governments taking place of Earth, which will unite all those peoples against the Cybermen. So the Cybermen have decided to break up the meeting, which makes sense. Turns out that little shoebox-sized bomb the Doctor deactivated in the caves was powerful enough to destroy everyone and everything on the planet's surface, proving that the Cybermen firmly believe that There Is No Kill Like Overkill. The Doctor thwarted their attempt to detonate the bomb, but the Cyber-Leader has a contingency plan — crash the freighter into Earth, and the explosion of its antimatter-fuelled reactor will have basically the same result.
Regardless, Tegan is captured and dragged to the bridge while Scott and a few other humans run around blowing up Cybermen... but spending most of their time hiding from them. The Doctor makes a show of bravado until Tegan is threatened, and the Cyber-Leader claims that this is the weakness of organics. The Doctor claims otherwise, wondering when the Cybermen enjoyed the laughter of a child or sat down to have a nice meal together. The Cyber-Leader also heads out to the TARDIS to make his escape with his lieutenant. At this time, Scott's Commandos break onto the Bridge and pretty much slaughter most of the Cybermen there. Unfortunately, Adric's attempt to bring the freighter out of hyperdrive goes spectacularly wrong and sends the freighter careening back in time, meaning that the Earth of the future may be safe but the Earth of the past (and thus, all future) is now in danger.
Adric decides to stay at the control console, trying to fix the problem before everyone dies. Scott's Commandos and Captain Briggs instead leap out into escape pods, while the Doctor and the two ladies head out to recapture the TARDIS from the Cybermen. Inside the TARDIS, the Cyber-Leader holds the Doctor and companions at gunpoint while they talk for a good length of time. The Cyber-Leader brags about how Earth will be wiped out, but the Doctor then realizes that they've gone back in time just over 65 million years. This means that the dinosaurs were wiped out by the freighter/bomb combination rather than any meteor or asteroid... but no one remembers to tell Adric this, and he is feverishly crunching numbers in an attempt to stop the ship.
Fed up with the talking, the Cyber-Leader decides to kill the TARDIS crew, but Tegan jumps on him and the Doctor breaks up Adric's golden badge all over its chest unit, but not before it shoots and damages the TARDIS console. And then the Doctor grabs the gun and shoots the Leader, killing it. Adric, for his part, is nearly done screwing up history when a lone, near-death Cyberman prevents him from entering the calculations by blowing up the console. The Doctor knows he can't save Adric, not just because he physically couldn't but also because it's likely the extinction of the dinosaurs is a fixed point, and we watch Adric's ship ram itself into the surface of the Earth, killing off all the Dinosaurs and making way for Man... with Adric along for the ride.
Tegan and Nyssa hold each other for comfort as the Doctor can only look on at the screen helplessly. Silent credits roll over Adric's broken badge...
- Action Girl: Nyssa and Tegan manage to kill one Cyberman each, though Tegan is captured moments later and then spends the final episode being held hostage by the Cyber-Leader. Plus, at least a third of the soldiers are female, instead of the usual token female guest star amongst an all-male battalion.
- All There in the Manual: Later expanded universe sources, Doctor Who: Cybermen and its audio adaptation The ArcHive Tapes, have In-Universe historians identify the version of Cybermen seen here and in later classic stories as CyberNeomorphs. It specifies that they were the result of the CyberNomads from "Revenge of the Cybermen" and a group of CyberTelosians from the tombs on Telos merging into one.
- Artistic Licence – Biology: Dinosaurs are described as a "species". As in, just one.
- Artistic Licence - Geography: Adric's ship seems to be heading straight for Korea, which apparently looks the same 65 million years ago as it did today — as does the rest of the Earth, in fact (the remastered special effects on the DVD fix this mistake). The location of the impact in the original is more forgivable, as the believed site of the meteorite impact that killed the dinosaurs was still nearly a decade away from being pinpointed at that time (Chicxulub crater was identified in 1990). It's only slightly off on the remastered version (the impact site of the freighter is solidly on present-day western Africa, near the split that separated it from the Americas, while Chicxulub is on the Yucatan peninsula, which would be the side with the Americas), but close enough.
- Batman Grabs a Gun: Evoked by Tegan and Scott when the latter hears laserfire and assumes it to be the Doctor. Tegan hopes this is not the case, as it would not be "the Doctor's style." Later the Doctor straight up shoots the Cyber Leader, however.
- BBC Quarry: One of the few serials of Doctor Who to feature a quarry that the Doctor and companions never visit.
- Been There, Shaped History: The Doctor and the Cybermen were responsible for the dinosaurs dying out.
- Beware the Nice Ones: You know things are extremely dire when Nyssa, a person from the most peaceful planet in the universe, chooses to pick up a gun and use it without hesitation.
- Big Bad: The Cyber-Leader.
- Bittersweet Ending: The Cybermen are stopped but at the cost of Adric's life.
- Blofeld Ploy: A Cyberman aims a gun at the Doctor... and then shoots Ringway.
- Boomerang Bigot: The Cyber-leader mocks the doctor about emotion, but he seem to show traits of it himself.
- The Bus Came Back: This was the first appearance of the Cybermen since "Revenge of the Cybermen" over seven years prior, which certainly added to the shock factor of suddenly seeing them at the end of Episode 1.
- Call-Back: In Adric's final moments, he's holding his brother's belt.
- Continuity Nod:
- The Doctor is reading ''Black Orchid'' before his argument with Adric.
- Amongst the objects in Adric's room is the skull mask worn by the Terileptil Android when it went out in public as the figure of Death, and one of the many pendants worn by the Kinda tribe's male members.
- Adric mentions the Monitor at Logopolis.
- Adric mentions that Romana is still in E-Space, and could help him if he returned.
- The Cyber Leader plays clips of the Doctor's previous encounters with them.
- The Corpse Stops Here: At the Doctor's and Adric's feet.
- Costume Evolution: The Cybermen are significantly redesigned, with more detailed heads and loose metallic coveralls reminiscent of contemporary military combat gear instead of the skin-tight suits of earlier designs. The teardrop motif that had been present since "The Wheel in Space" is also removed, reverting to the purely circular eyes used from "The Tenth Planet" to "The Tomb of the Cybermen". This redesign would remain in place until "Rise of the Cybermen" 24 years later.
- Creepy Monotone: Played straight (sort of), but ONLY by the regular Cybers. The Leader sounds, er... very emotional at some bits, due to actor David Banks having a Cybermen obsession. (He would go on to write and record a four-hour comprehensive history of the species, just for the heck of it.)
- Cry into Chest: Tegan and Nyssa cry on each other's shoulders following Adric's death.
- A Day in the Limelight: Each of the Doctor's companions was given a story where they could take a bigger role this season. This is Adric's. He gets the Heroic Sacrifice, the first since Katarina and Sara Kingdom back in season three.
- Death of a Child: Adric, if this trope is extended to include teenagers.
- Downer Ending: Adric's death to some. To make matters worse he died thinking he failed to save the past, not knowing that the ship he was on was the 'asteroid' that wiped out the dinosaurs, leading to humanity's rise.
- Dying Moment of Awesome: Adric valiantly trying to stop the freighter from crashing.
- Enhanced on DVD: The story ends, as we all know by now, with the freighter ship crashing into prehistoric Earth with Adric aboard, killing both him and the dinosaurs on the planet. However, the drama is heavily overshadowed by how the crash scene plays out: the image of Earth used is of modern Earth rather than prehistoric Earth, the freighter is just a still image on the TARDIS monitor, and the "explosion" is just a bunch of Atari-esque pink & white flashing lights. The DVD enhancement changes the image of Earth to (what is generally accepted as) prehistoric Earth, which the new, CGI freighter visibly slams into. The TARDIS's broadcast of the explosion now shows a yellow-white flash over the impact site with a reasonably large shockwave, and the way it plays out delivers the same wham that the writers intended.
- On a slightly related note, the freighter itself and its escape pods are given CGI makeovers as well.
- Face Death with Dignity: Realizing he's doomed, Adric calmly awaits the crash of the freighter once the last Cyberman on-board blows up the console he was working at.
- Failed a Spot Check: In the first episode, a pair of assassin robots dart down a corridor just before a soldier turns to look. While the robots themselves are out of view, their shadows are clearly visible retreating down the passage; however, the soldier completely fails to notice despite staring straight at them.
- Flashback: The Cyberleader gives his lieutenant a brief history of their encounters with the Doctor. Clips from "The Tenth Planet", "The Wheel in Space" and "Revenge of the Cybermen" are shown, though the Cyberleader mentions the events depicted in "The Tomb of the Cybermen" rather than "The Wheel in Space" as "The Tomb of the Cybermen" was missing at the time and would not be found for another ten years.
- Foreshadowing: The Doctor while looking at dinosaur fossils says he always meant to go back and find out what killed them.
- Ham-to-Ham Combat: Whenever the 1980s version of the Cyber-Leader is involved, expect wall-to-wall scene chewing from at least one other actor. Such as Peter Davison in this serial, who tries to out-ham his enemy with all he can muster.
- Heroic Sacrifice: Ultimately, Adric failed in his goal (and achieving it would have been impossible without a major paradox being created), but he was trying to be heroic. Technically, he didn't fail completely — his actions prevented the entire population of the earth from being killed. Well, the human population, anyway.
- Informed Attribute: The Cybermen are supposed to be emotionless. It is not apparent. This is lampshaded by the Doctor:"Compared to some, this one's positively flippant".
- Irony: Dramatic Irony, to be exact. The Doctor and the audience know that it's fine for the freighter to crash into earth and that there's no way to avoid it anyway. Adric does not and continues doing everything he can to try to prevent it, thinking he needs to in order to save humanity.
- Jerkass: Part of the reason Ringway betrays everyone is that Captain Briggs is not a very nice person, and seems to care more about making sure she gets her bonus than her crew's lives.
- Killed Off for Real: Being blown to shreds and scattered across the prehistoric Earth will do that to you. (Although the Big Finish audio "The Boy That Time Forgot" gave Adric a different fate in the end). Incidentally, this was the third and final instance of a classic series companion being killed, unless you count Kamelion, and Peri's death-that-wasn't.
- Large Ham:
The Doctor: Compared to some, this one is positively flippant.
- The Cyber-Leader, of all people. "My army awaits, DOCTORRR!" Throughout the episode, he displays anger, pride, irritation, even malicious smugness. It's even lampshaded by the Doctor:
- Even a single word sentence from the Cyber-Leader becomes hamtastic, thanks to how it's read out each and every single time: "Excellent!"
- The Doctor wants to announce his PRESENCE.
- Last Breath Bullet: one cyberman recovers just enough to destroy Adric's control panel. In the Tardis at the same time, the Cyber-leader spends his death-throes firing.
- Left Hanging: The surviving crew members of the freighter escape in their lifepod but it happens after they time travel to prehistoric Earth. The last we hear of them is Lt. Scott informing the TARDIS crew by radio that Adric wasn't on the lifepod with them. They are promptly forgotten about in the wake of Adric's death, and their fate isn't revealed until the following story, "Time-Flight", where Nyssa mentions in passing that they returned the crew to their own time. This wouldn't have been so problematic at the time, since stories in this era often used the first episode of the following serial to tie up any loose ends, but with the VHS and DVD releases of this story and "Time-Flight" being separated by several years, it left more than a few modern-era viewers wondering What Happened to the Mouse?.
- Let's Split Up, Gang!: The troopers actually stick together until one of them gets wounded and is sent back to the surface under escort. When they go missing (and so does the trooper who went from the surface to help them), another group is sent back to investigate. Everyone that leaves the main party finds a gruesome end at the hands of the Cybermen's androids.
- Nice Job Breaking It, Hero: The Doctor indirectly caused the extinction of the dinosaurs.
- Ooh, Me Accent's Slipping: James Warwick changes Lt. Scott's accent without narrative cause. There's a clear and inexplicable difference between his work on location, and his later-recorded scenes in the studio. This fact was remarked upon by Janet Fielding and Peter Davison on the DVD commentary.
- Phlebotinum Killed the Dinosaurs: Turns out the ship that crashes into Earth (with Adric still on it) was the supposed meteor that killed the Dinosaurs.
- Plot-Driven Breakdown: The TARDIS' controls get damaged at the worst possible time...
- Pyrrhic Victory: The Cyberleader's line (said in response to the Doctor's declaration that the Cybermen's plan to destroy the conference taking place on 26th Century Earth has been thwarted) about the Doctor "not enjoying the victory" turns out to be chillingly prophetic. The Doctor's victory over the Cybermen is overshadowed by Adric's death.
- Rewarded as a Traitor Deserves: Subverted; the Cybermen don't kill Ringway because of his treachery or because of his betraying his own crew, but rather because they mistakenly believe that he betrayed them.
- Sealed Army in a Can: The Cyberarmy on the cargo ship.
- Senseless Sacrifice: Adric attempts to save the earth by diverting the course of the freighter headed right for it. What he doesn't realize is that the freighter crashing into the earth is what caused the extinction of the dinosaurs. He fails.
- Sensor Suspense: The expedition base camp has a scanner that shows life-signs moving around in the cave system the expedition is exploring. Over the course of the first episode we get dots suddenly disappearing (expedition members being killed), a dot that fades in and out (the thing that's killing them, which is alien enough to confuse the scanner), and dots suddenly appearing (the Doctor and friends arriving, just in time to be accused of the murders).
- Shout-Out: The Cyberman caught in the ship's door recalls Han Solo frozen in carbonite.
- Silent Credits: At the end of the last part. They were John Nathan-Turner's idea, nicked from Coronation Street.
- Stable Time Loop: The freighter is sent back in time and causes the extinction of the dinosaurs, the dominance of Homo sapiens and the creation of the ship. It also kills Adric.
- Stunned Silence: Played for Drama at the end as the Doctor is stunned into silence following Adric's death while Nyssa and Tegan are sobbing. It's like he has no idea how to react.
- Surprisingly Realistic Outcome: The Doctor's jovial flippancy doesn't fly well with a hardened military officer who's just had several of his men killed.Too many people have died for you to play the fool.
- Taking You with Me: Just before a Cyberman dies it shoots the controls, meaning Adric can't pilot the ship away.
- Tempting Fate: The Doctor and Adric get into an argument when Adric demands to go home, but the Doctor says he won't risk taking the TARDIS back into E-Space. At one point, the Doctor tells Adric: "I'm not hanging around while you plot the course to your own destruction!" Then, at the end of Episode Four, Adric gets blown up.
- Thousand-Yard Stare: In the denouement, the Doctor turns to stone while Tegan, almost penitently, demands some sort of miracle from him and receives none.
- Trailers Always Spoil: Averted to truly heroic levels. Showrunner John Nathan-Turner went to enormous lengths to keep the Cybermen's return secret, resulting in a famous Oh, Crap! moment at the end of Episode 1. Nathan-Turner actually turned down a cover shoot with the Cybermen for the Radio Times in order to keep the secret as secret as possible (despite the fact that a Radio Times cover was quite prestigious, and Who had not had one for nearly a decade), also insisted the cast listings in the same magazine referred to the Cyber Leader and Cyber Lieutenant as just "Leader" and "Lieutenant", etc. In addition, he put a scene for Adric in the next story so he would be present in the listings that came out the week the second half of the story aired... hiding his death in this one. It's only spoiled to modern viewers, as there's a Cyberman on the DVD cover.
- Two of Your Earth Minutes: Adric tells Nyssa what year it is "in the time scale you call Anno Domini", i.e. Earth years, even though Nyssa is no more from Earth than he is. To be fair, Tegan, who is from Earth, is also present.ADRIC: The year is 2526 in the time scale you call Anno Domini.
- We Meet Again:Cyberleader: So, we meet again, Doctor!
- Wham Episode: Companion death has always been very rare, and the ones that have died in the past (and future) were all one-story companions, with the exception of one who joined at the end of one story and died early in the next. This marks the first time in the show's history that a main cast member of the show has been completely and unambiguously killed off, something which still hasn't been repeated as of 2023. It's THAT rare. "Earthshock" intensified the effect by silently rolling the credits over a picture of Adric's badge, smashed beyond repair. While that's the biggest Wham part of this serial, it also has an earlier shocker: Back when it first aired, the Cybermen being the villains was a well kept secret. But both twists have suffered It Was His Sled at this point.
- Wham Shot: The Reveal of the masters of the killer androids at the end of the first episode- the Cybermen. While it may not seem like much of a twist to modern viewers, the Cybermen hadn't been seen by Doctor Who viewers for seven years, since 1975's "Revenge of the Cybermen".
- Why Don't You Just Shoot Him?: When Briggs asks this, the Cyberleader says he wants his guards to watch the reactions of the crew for scientific reasons, so they can understand human weaknesses.
- You Have Outlived Your Usefulness: Amusingly subverted. It appears that the Cybermen initially intend to honour their deal with Ringway, but when Scott's troopers arrive on the freighter and start shooting up the place, the Cyber-Leader wrongly assumes that these are extra crewmembers who Ringway was trying to hide the existence of, and kills him at the next opportunity.