Captain Hart: Yes... a pretty impulsive fellow. If one can believe the history books.
The Doctor: History books? Captain Hart, Horatio Nelson was a personal friend of mine.
The one with the electric farting music.
The Doctor and Jo visit the Master in his high-security offshore prison and find out that ships have been disappearing at sea. The Doctor investigates, and learns that the sinkings appear to centre around an abandoned sea fort. Heading out there, they encounter what one sailor calls a "Sea Devil" — apparently an amphibious breed of "Silurian" (see "The Silurians"). In fact, the Doctor hangs a lampshade on an error in the previous serial by pointing out that the discoverer got the name wrong — the creatures are from the Eocene period, not the Silurian.
It turns out that the Master has the prison governor under control. The latter is procuring parts so that the renegade Time Lord can build a machine to revive the Sea Devils from hibernation. Jo sneaks around to rescue the Doctor, and the Doctor engages the Master in an awesome fencing battle, disarms him, holds him at swordpoint and munches down on the Master's lunch before tossing him back his sword simply because he's having too much damned fun.
Using cars, boats, stock footage of a helicopter, a close-up toy submarine and one giant actual ship, the Doctor tries to establish contact with the creatures. He goes down in a diving bell to try and negotiate with the Sea Devils, but politicians have got involved now and a depth-charge attack soon disrupts to negotiations. In the confusion, the Doctor frees a captured British submarine and heads back to the surface.
The Sea Devils attack and capture the nearby naval base and with it the Doctor, who is taken to the Master and forced to help him finish the machine. But the Doctor sabotages it, and the two Time Lords get away on jet skis. The Sea Devils are all killed in the explosion, but the Master makes his escape in a hovercraft.
- Absentee Actor: Nicholas Courtney doesn't appear at all, Captain Hart more or less taking his role.
- Action Girl: Jo Grant is one in this episode. She rescues the Doctor, incapacitates a guard and pilots a hovercraft.
- Adorkable: The Master, of all people, has a brief moment of this when he watches a children's puppet show (and confuses the puppets for aliens).
- Aliens Steal Cable: The Master is somewhat enamoured with The Clangers.
- As You Know: The Master says this while explaining to the Doctor the Sea Devils' plan.
- Author Appeal: More like Actor Appeal, really: Jon Pertwee was, according to accounts, in seventh heaven during the filming of this serial, as a number of vehicle sequences were written in expressly for his benefit, including a jet-ski chase.
- And mortified Roger Delgado - who was deathly afraid of the sea, but did his stunts anyway like trooper.
- Air-Vent Passageway: Jo climbs into the ventilation shaft and onto the roof after the Sea Devils have chucked her, Captain Hart and the Personal Parliamentary Secretary in a room.
- Bang, Bang, BANG: Averted. Genuine Royal Navy ordnance is shot off (including a Bofors anti-aircraft cannon), but the soft (for varying values of "soft", of course) "paf-paf" sound that the real guns actually have on camera is nothing like what an audience might expect.
- Bittersweet Ending: The world is saved but the Sea Devils, who weren't bad, just misled, are destroyed and the Master, who caused all this, escapes.
- The Brigadier: Not, for once, the Brigadier, but Captain Hart.
- Chromosome Casting: Aside from Jo, the only female character in the story is 3rd Officer Jane Blythe.
- Creator Cameo: This serial's director, Michael Briant, provided the voice of the radio DJ in episode two.
- Crystal Clear Picture: The Clangers: the picture is inserted via yellowscreen (yellow was the preferred matte color for BBC Chromakey work in the '70s).
- Death Equals Redemption: Redemption from being an Unwitting Pawn (and all-round dumbass) rather than being evil, but Trenchard spends his last moments buying some time for his guards to escape and making a futile attempt to keep the Sea Devils away from the Master.
- Enemy Eats Your Lunch: During the fencing fight, the Doctor disarms the Master, steals his sandwich at swordpoint and eats it. He later steals Jo's sandwich too, the swine!
- Excuse Me While I Multitask: During the fencing fight, the Doctor disarms the Master, steals his sandwich at swordpoint and eats it.
- Exposed Extraterrestrials: The Sea Devils had to be given string vests at the last minute as someone objected to this issue late into production.
- Fake Shemp: In the jetski chase, the Master is played by a stunt double, which is why he tries to keep his face hidden.
- Fish People: The clue's in the title.
- Flynning: During their sword fight, after the Master disarms the Doctor, and has him pinned in a corner ready to deliver the killing blow, the Doctor escapes by kicking the Master back.
- For the Evulz: The Master flat-out admits he's only working with the villains so they can get rid of "the human race of which you are so very fond."
- Go-Karting with Bowser: The Doctor, Jo and The Master share a couple of jokes and chat amiably for a few minutes when The Doctor and Jo first arrive.
- Hazardous Water: The Sea Devils make every attempt to turn the North Sea into this.
- Humans Are Warriors: The Doctor tells the Sea Devils that attacking the humans would be a bad idea because of this.
- I Did What I Had to Do: The Doctor at the end.
- Idiot Ball:
- The Master forces the Doctor to help him fix a gadget. And genuinely expected that to go just fine. To be fair, the Master thought he could threaten the Doctor's companions as leverage, but as soon as they were safe and sound, his plan backfired entirely.
- Right at the very end, the script punts the ball squarely in the Doctor and the Navy's direction, and they catch it. This one happens to be a fastball and nobody really saw it coming because of how unbelievable the Karma Houdini trick the Master pulled was. The Navy has the Master under guard, with The Doctor watching, on a relatively small hovercraft. Somehow, even among all those sailors and one Time Lord, in a confined space, The Master is able to a) hypnotize a sailor into playing dead, b) slap a perfect mask of his face onto the poor schlub, and c) swap clothes with him. And then, he's able to make off with the hovercraft, because the Navy decided not to have at least two people mind it. (Though admittedly that last bit might have also been the master using hypnotism on getting said two people out.)
- Improperly Placed Firearms: The prison guards are armed with Combloc SKS rifles.
- Jedi Mind Trick: You can almost hear "these aren't the droids you're looking for" as The Master hypnotizes a CPO set to guard him in the last episode.
- Karma Houdini: The Master
- Kingpin in His Gym: Played for laughs when the Master, locked up in a sea fortress, exercises on a rowing machine. It doesn't seem to be working, though — the Doctor remarks that the Master has put on weight!
- Klingons Love Shakespeare: The Master enjoys The Clangers of all things.
- Last Chance to Quit: The Doctor gives one to the Sea Devils. To his regret, they refuse.
- Latex Perfection: The Master pulls one of these, along with another faked death, to escape at the end of the episode.
- Lima Syndrome: Colonel Trenchard falls under the Master's influence without even needing to be hypnotised.
- The Master
- Master Swordsman: The Doctor is able to out-fight the Master in a fencing duel. He then eats a sandwich while holding the Master at swordpoint. A sandwich that happened to be the Master's lunch. And then he throws the Master back his sword so they can have some more fun.
- Mistook the Dominant Lifeform: The Master mistakes The Clangers for actual aliens. (an Alternate Character Interpretation, supported by watching the Master's reactions carefully, suggests that he knew full well that The Clangers was a TV show, but was toying with Trenchard by playing dumb.)
- As an ALTERNATE Alternate Character Interpretation, the Master knew it was a children's show and was briefly amused by it: he's smiling and whistling along as he watches. Trenchard enters and catches him, and the Master has to pretend not to understand what he's watching in order to save face. His "Oh~" when he's informed that they're just puppets is said in that sort of false, semi-interested tone you use when someone tells you something you already know but you're being polite. He casually crosses the room to switch the TV off, and then out of Trenchard's view grimaces in exasperation at having to turn off a program he was enjoying.
- Noodle Incident: The Doctor lets on that he was a close personal friend of Admiral Lord Nelson.
- Obvious Stunt Double: In the scene where the Doctor and Jo arrive at the sea fort, Jo is clearly not being played by Katy Manning (in fact, the stunt double is a man, stunt regular Stuart Fell).
- Office Golf: Colonel Trenchard seems to be fond of this. The Doctor has a go, too, but he does it blindfolded.
- Off-the-Shelf FX: That little nuclear sub? A modified toy from Woolworth's.
- ... that was apparently so convincing looking that it got the production team in trouble with the Navy, as they were concerned that top secret designs were just leaked on national television!
- Play-Along Prisoner: The Doctor pays the Master a visit, finding that he's rather content and resigned to his certainly centuries of confinement... because, as he later finds out, he's got the entire prison staff working for him and is just biding his time before he unleashes the Sea Devils.
- Reality Is Unrealistic: The Bofors gun firing in the last episode, and many of the rifles throughout, don't seem to have their sounds adjusted, and were recorded as they'd naturally sound, making for a less-than-dramatic effect for those unaccustomed to how guns actually sound when fired.
- Refuge in Audacity: Averted. When trying to rent the launch from the quaymaster, The Doctor mentions that his leg was injured in The Crimea. The quaymaster doesn't buy it. Then he tries Gallipoli. Still no luck. Finally he tries El Alamein, by which time he gives up and says "It really doesn't matter, does it?"
- Retcon: The Doctor points out that the cave creatures from "Doctor Who and the Silurians" should have, in fact, been named the "Eocenes" instead of the "Silurians," because of the epoch they originated from, which is the real-life author (same for both stories) correcting his earlier mistake when he was called on it after the broadcast of the first story. Unfortunately, it's highly unlikely that that they could have come from the Eocene period, either.
- Reverse Polarity: The Doctor sabotages the Master's machine by "reversing the polarity of the neutron flow". This is the only time the Third Doctor utters the whole phrase instead of just parts of it.Doctor: Before you reactivated it, I reversed the polarity of the neutron flow.
- Scare Chord: A jarring, grinding, beeping sound is the first cue on this story's soundtrack. Have a listen to see if you can describe it any better.
- Sequel Episode: To "The Silurians".
- Shout-Out:Master: Do you know who I am?Guard: You're The Prisoner.
- Which might explain why his guards all wear cloaks and badges, and drive about in quirky white cars.
- Shout-Out to Shakespeare: Walker quotes Hamlet: "Cry havoc and let slip the dogs of war".
- Stock Footage: A helicopter changes make and color so that it can blow up via stock footage.
- Sword Fight: Consisting of the Doctor disarming the Master, holding him at swordpoint as the Doctor munches down on the Master's lunch and then tossing the Master back his sword simply because he's having too much damned fun.
- Unnecessary Combat Roll: A postmortem one when a Sea Devil played by Stuart Fell does a backflip when shot.
- Unspoken Plan Guarantee: Played With when Jo comes up with a plan to break the Doctor out of prison. We do see her telling the Doctor, but since she's stuck on the other side of some soundproofed glass at the time we see her communicate the plan through mime. It's just difficult enough to understand that when we see the Doctor and Jo perform parts of it, it feels less like a spoiler and more like, "oh, that's what that hand gesture meant".
- Villains Out Shopping: The Master whistles along to the Clangers.It seems to be a rather interesting extraterrestrial life form.
- Visible Boom Mic: During the minefield scene the Doctor appears to fend off a boom mike with his sonic screwdriver.
- Why Does it Have to be Water?: According to the crew, Roger Delgado was not happy at all about having to float in the ocean for the rescue scene (while fear is stretching it a bit, the crew recalled him being extremely uncomfortable around water). For the skiboat chase, they had to have Jon Pertwee chase a stunt double, as Delgado flat-out refused to shoot the sequence.
- Besides being afraid of the water, Delgado couldn't swim.
- You Have Outlived Your Usefulness: While the Master never outright says this to Trenchard, the trope is demonstrated in him not warning Trenchard about the impending Sea Devil attack, nor even reacting upon seeing his dead body.