The one with the cursed production.
The Time Ring gets the Doctor and companions back to Nerva Beacon all right — but at the wrong time (typical shoddy Time Lord tech), instead putting them many millennia earlier than their previous visit. At this time, the station is an active radio beacon controlling space traffic around Earth, particularly with reference to a new asteroid in orbit around Jupiter - a "planet of gold" called Voga. However, all is not going well. A space plague is rife on the station and has killed all but a few of the crew, and the Doctor and friends are of course immediately suspected.
The space plague turns out to be poison, spread by a traitorous scientist, Dr. Kellman, on behalf of the Cybermen. They want to destroy Voga because of their weakness to gold. Sarah Jane is infected with the plague, but she's cured by Harry through the use of a transmat system. Upon their arrival on Voga, they're captured by Vogans (no, not those Vogons) working for the power-hungry head of security, Vorus. Vorus is confronted by the Vogan leader, Tyrum, who chastises him for making contact with humans. The Vogans have been strictly isolationist for centuries because their planet was nearly destroyed by Cybermen in the last war. Vorus insists on taking action, leading to a brief civil war between his faction and Tyrum's.
When the Cybermen arrive, the Doctor and the remaining crew from the beacon are forced to carry Cyber bombs into the heart of Voga, but the Doctor exploits the Cybermen's radar system and rids himself of his bomb to make contact with the Vogans. It seems that Kellman is in fact working for Vorus, luring the Cybermen onto Nerva Beacon, which the Vorus had planned to destroy with their Skystriker rocket. The Doctor returns to the beacon to save Sarah Jane, who had returned there to save him. Despite clever repurposing of a Cybermat to attack the Cybermen, the Doctor is captured.
The Cybermen, realizing their plan has failed, load the beacon with explosives and aim it for Voga, evacuating and leaving the Doctor and Sarah Jane aboard to die. The Skystriker is launched (well, a painfully obvious Saturn V rocket being palmed off as a Vogan anti-Cyberman rocket is launched), but the Vogans manage to divert it to hit the Cybermen's ship. Though the Cybermen locked the controls of the beacon before their departure, the Doctor manages to enable the secondary controls just in time to keep the beacon from destroying Voga.
The TARDIS appears back on the station, having been sent to catch up with them by the Time Lords, and on boarding the ship, the Doctor receives a message from The Brigadier, requesting assistance back on Earth...
The only appearance of the Cybermen in the Seventies, and the only Tom Baker episode to feature them. They hadn't appeared since the Second Doctor's "The Invasion" and wouldn't return again until "Earthshock". The serial was written by Cyberman creator Gerry Davis and had uncredited rewrites by script editor Robert Holmes. This was also the first story to be released on home video.
- Actor Allusion:
- Butt-Monkey: "HARRY SULLIVAN IS AN IMBECILE!"
- The Cavalry: Sarah and Harry are cornered in the caves by Vorus' guards who are about to kill them, when a voice calls out they are surrounded and orders them to put their guns down. This is Tyrum's militia who step out of hiding and reveal they have the guards surrounded.
- Chromosome Casting: Sarah is the only female character in the story.
- City of Gold: The asteroid Voga is the "planet of gold".
- Corpsing: It apparently took tens of takes before Tom Baker was able to deliver the line "We're headed for the biggest bang in history" without Elisabeth Sladen - and most of the floor crew - disintegrating into hysterics. (The writers had missed the Double Entendre, and intended it as a completely straight Wham Line.)
- Covers Always Lie: This was the first serial to be released by BBC Video, but the cover had the logo & a Cybermen of the early '80s.
- Double Reverse Quadruple Agent: Kellman.
- Divided We Fall/Enemy Mine: When it becomes clear that the Cybermen will overrun Voga, Vorus and Tyrum's forces declare a truce to better defend themselves.
- Ghost Ship: Nerva Beacon is all but this when the TARDIS crew arrive.
- Heartbeat Soundtrack: The sound of a (human, not Time Lord) heartbeat plays over the bomb scenes.
- Heroic Sacrifice: One of the surviving Beacon crew sacrifices himself to destroy the Cybermen on Voga, buying the Doctor and Harry time to save Sarah Jane.
- Imperial Stormtrooper Marksmanship Academy: Oddly not the Cyberman this time, who display excellent aim as they mow down ranks of Vogan soldiers. The Vogans, however, are terrible shots, seemingly unable to hit a target at more than point blank range, and missing Harry by at least three feet when shooting at him.
- Informed Attribute: From now until the end of the classic series, the Cybermen's supposedly emotionless nature would become this, with the Cyber-Leader getting visibly angry any time his plans go wrong, bragging about the power of their Cyber-Bombs, and sadistically mocking the Doctor and Sarah over Nerva's impending crash into Voga.
- Keystone Army: The Cybermen appear to be under the impression that by destroying Voga and its massive gold supply, the galaxy will be defenseless against them. Nobody ever brings up the fact that even if Voga is the galaxy's largest source of gold, it is hardly the only source of gold, and that if a small pouch of gold can kill a Cyberman, worlds with far more meager supplies of gold could still make glitter guns and fight back against them.
- Kill 'Em All: Of the human characters in the story, only Commander Stevenson survives. The Vogans also end up with a high body count while fighting the Cybermen invaders.
- Large Ham: The Cyber-Leader in this story somehow manages to out-ham his 1980s counterpart.
- Mexican Standoff: The Doctor briefly sets up one in the third episode by stealing a Cyberbomb and threatening to explode it if anyone comes near him. The Cyber-Leader defuses the situation by just remotely signalling a Cyberman to ambush the Doctor from behind.
- Only in It for the Money: Kellman's true loyalty is with Voga's gold.
- The Plague: The reason why Nerva Beacon is in quarantine, and what killed most of their crew. Though, in fact it is not a plague at all.
- Planet of Gold: Voga.
- Redemption Equals Death: Kellman's last action is to push Harry out of the path of a rockfall, getting fatally caught in it himself.
- The Remnant: The Cybermen encountered are small group of stragglers from the Cyber War reduced to skulking about the galaxy in a worn-out warship.
- Reptiles Are Abhorrent: The Cybermats have a more snake-like design compared to their earlier, mouse-like design.
- Retcon: The swirly symbol later became the Seal Of Rassilon. Word of God has it that the Time Lords visited Voga once, and the Vogans liked the design.
- Same Plot Sequel: The story is a near-remake of "The Moonbase": Cybermen using a fake plague attack a human outpost somewhere in the solar system intending to use it as a base for an attack on another planet.
- Screen Shake: Used during the scene where the Nerva Beacon almost crashes.
- Shout-Out to Shakespeare: The Doctor paraphrases Macbeth:Dusty death. Out, out with.
- Sigil Spam: The Vogans have their swirly symbol (that would later become the Seal of Rassilon) plastered all over their city: showing up on uniforms, as wall decorations, inscribed into furniture, etc.
- Stock Footage: In one of the most blatant ever uses, a video of a Saturn V taking off was used to represent the launch of a rocket that looked nothing like it.
- Stock Poses: The Doctor, Lester and Stephenson pull off The Three Monkeys pose while prisoners of the Cybermen.
- Strapped to a Bomb: The Cybermen strap bombs to the Doctor and the surviving members of the beacon crew and force them to march into the heart of Voga.
- Tainted Veins: A symptom of the "space plague" — which the Doctor finds suspiciously similar to a "space plague" he's seen before.
- Too Dumb to Live: The Vogans. They know the Cybermen have a weakness to gold, which exists in ample quantities on Voga, but they never get the idea to exploit it, even when several of them are getting slaughtered by two Cybermen.
- Unnecessarily Large Vessel: A space station that normally has a crew of 50 is being run by a crew of three, the rest having died from a plague.
- Unusual Weapon Mounting: The Cybermen head guns.
- Voga-Shattering Kaboom: The Cybermen's plan is to blow up Voga.
- Weaksauce Weakness: The Cybermen's "allergy" to gold is first introduced in this story. Here, because it is an efficient conductor of electricity, getting gold dust in their chest units shorts them out, making it impossible for the Cybermen to breathe. It would become much more ridiculous in future appearances.
- Worthless Yellow Rocks: The reason Kellman is working for the Vogans.
- You Have Outlived Your Usefulness: The Doctor knows the Cybermen are going to kill their prisoners as soon as they planted the bombs and drops the trope name almost literally.
- The X of Y: An infamous one, since the supposedly emotionless Cybermen should not be capable of feeling the desire for revenge. Word of God is that the Vogans incorrectly assume this to be the Cybermen's motive, but in reality they're just taking the entirely logical step of eliminating the threat that caused them to lose their previous war before starting a new one.