The one where Middle Age warlords meet a talking potato. Oh, and the one where we meet the woman who first etched herself on the Doctor's (and Whovians') hearts.
An intrepid investigative journalist, Sarah Jane Smith, infiltrates a secret research centre where a number of top scientists are being held in protective custody while UNIT investigates the disappearance of some of their colleagues.
The Doctor follows the trail back to The Middle Ages in the TARDIS; unbeknownst to him, Sarah Jane has stowed away on board. It seems that a robber baron called Irongron has made a deal with Linx, a Sontaran of the Sontaran Army Space Corps. Linx gives Irongron advanced weapons in exchange for time and shelter while repairing his damaged spacecraft. The kidnapped scientists are working under hypnosis to help.
The Doctor helps local lord Sir Edward of Wessex to repel an attack by Irongron's men, then drugs the food in Irongron's castle in order to remove the advanced weapons while they sleep. With the help of one of the scientists, the Doctor then sends the scientists back to the 20th century.
Linx kills Irongron and is about to leave when he is shot in the back of the neck with an arrow by Hal, one of Wessex's archers. Turns out that's the only weak spot on a Sontaran's armour - the "probic vent" - and he dies. The Doctor, Sarah and Hal escape before the ship can explode and destroy Irongron's castle.
An official BBC radio play by Barry Letts, "The Paradise of Death", takes place between this episode and the next and stars Three, Sarah Jane and the Brigadier.
- Absent-Minded Professor: Professor Rubeish.
- Achilles' Heel: The Sontaran's probic vent.
- Anachronism Stew: It's implied that the action may be taking place pre-1066 ("Wessex," as a place name, was quickly dispensed with after the Norman Conquest), but the armor and weapons look to be anywhere between the 13 to 15th centuries.
- Animated Armor: Linx builds a robot knight for Irongron, but when the control unit gets damaged it turns on his men. The Doctor decides to impersonate another robot, but this backfires when Irongron decides to test the robot's skill by fighting it.
- Armor-Piercing Slap: Irongron gets a nasty surprise when he tries to manhandle Linx and gets knocked across the room by the Heavy Worlder.
- Blasting It Out of Their Hands: Once by Linx with his hand laser, and more impressively, Hal shooting an axe out of Irongron's hand with a bow.
- Blind Without 'Em: Prof. Rubeish. He fashions himself a monocle using Linx's equipment.
- Borrowed Catchphrase: The Brigadier says, "Oh, my giddy aunt" when he learns Professor Rubeish is missing, a phrase that was commonly spoken by the Second Doctor.
- Bullet-Proof Fashion Plate: After spending days in the middle ages, exercising (and presumably sweating) and rolling around in the dirt and straw, the Doctor's clothing is still immaculate.
- Call-Forward/Call-Back: The Doctor remembers the last time he met a Sontaran, but the actual events behind the meeting wouldn't be shown on TV for another 20 years.
- Chandelier Swing: The Doctor does one during a fight with Irongron's men.
- Cut His Heart Out with a Spoon:Irongron: I'll chop him up so fine, not even a sparrow will fill its beak!
- Dramatic Unmask: Happens twice In-Universe to Irongron; first when he catches sight of a Sontaran with his helmet off, then when the robot warrior he's fighting turns out to be the Doctor.
- Enhanced on DVD: The special release adds a starburst glow and laser blast effect to the orange tip of Linx's Sontaran hand laser device that makes it more apparent when it's activating, and replaces the exterior shot of an explosion going off that implies the castle Irongron sacked blew up (the series didn't have the budget or technology back then to show a castle properly explode) with a CGI effect where it is actually shown to be blown apart as everyone runs for cover.
- Establishing Character Moment: Sarah is introduced infiltrating UNIT by impersonating her aunt and getting belligerent when the Doctor asks her to make coffee.
- Evolving Credits: This episode debuts the opening sequence used until Three's finale, when it was modified to become Tom Baker's intro for all but his final season.
- Fire-Forged Friends: The Doctor and Sarah start off not liking or trusting each other much. Battling Linx together marks the beginning of a beautiful friendship.
- Firing Squad: Irongron puts the Doctor in front of an impromptu firing squad so his men can have some target practice with their new firearms (thus possibly becoming the first firing squad in Earth's history).
- Fish out of Temporal Water: Sarah Jane.
- The Gadfly: The Doctor enjoys himself trolling feminist Sarah Jane with sexist remarks.
- Getting Crap Past the Radar: When the Doctor says he has to go find a young girl (Sarah Jane), Prof. Rubeish says to himself: "Young girl? Should have thought he was a bit old for that sort of thing."
- Giving Radio to the Romans: Though unlike other examples of this trope, it's simply a means of buying off Irongron. Also, despite his own advanced technology, Linx has no intention of giving Irongron any more than the bare minimum to impress him in the form of crude black powder firearms. The Doctor still worries about the long term effects of giving these warlike humans advanced weaponry before their time.
- Going for the Big Scoop: Sarah Jane.
- Historical In-Joke: The Doctor describes Linx as "nasty, brutish and short", just like life in the Middle Ages (actually the quote is from Hobbes Leviathan).
- Humans Are Ugly: Irongron recoils in horror at the sight of Linx without his helmet, who snarks in response that his appearance isn't particularly pleasing to a Sontaran either.
- Imperial Stormtrooper Marksmanship Academy: The knaves of Irongron, and Irongron himself, can't hit anything with their new 'star weapons'. Doesn't really discourage them from having fun with them, if a bit frustrating when actually in battle. Justified as older rifles weren't very accurate and the men firing them had normally fought with medieval weapons and had never seen a gun before. They decide to kill the Doctor via firing squad as aiming practice.Irongrad: [amused] These knaves of mine aim so ill, Doctor, you are mayhap safer to stand still.
- Improbable Aiming Skills: Hal the archer can put an arrow through a probic vent from quite a ways away.
- I Need a Freaking Drink: A caffeine variation; when the Doctor reveals to Sarah Jane that he is an alien time-traveler, after a moment's shock she announces, "I could murder a cuppa tea!"
- Informed Ability: The Doctor's 'skilled' swordplay.
- Instant Sedation: Inverted. The drugged food takes a minute or so to knock out the people who ate it, but they are awakened with just a shake and a warning the castle is going to blow up.
- Intrepid Reporter: Sarah Jane.
- It Amused Me:
- Blood Knight that he is, Linx has no problem giving some primitives advanced weaponry so they can attack their rivals. The Doctor compares him to a little boy stirring up an ant hill to stop himself from getting bored.
- The guards let the Doctor and Sarah enter the castle posing as monks seeking alms, then have a good chuckle over how Irongron will react to them.
- Jabba Table Manners: The Doctor decides to toss away a bone while feasting, and gets a Disapproving Look from Sarah.
- Laughably Evil: Irongron and Bloodaxe are a damn goofy couple of guys.
- Magic from Technology: Both Linx and the Doctor are seen as wizards by the locals.
- MayDecember Romance: Rubeish mistakes the Doctor's interest in Sarah as this. Probably because he's eccentric, a bit of a distracted klutz, and prone to letting his thoughts meander into La La Land.
- The Middle Ages: Sarah Jane seems to think it's The Dung Ages, when she's not convinced it's actually a Renaissance Fair.
- Mind Control: Linx does this to the scientists.
- People in Rubber Suits: Linx.
- Professional Butt-Kisser: Bloodaxe asks Irongron why he doesn't just kill Linx. Irongron claims it's a matter of High Strategy, that's he's waiting to the right moment to strike after Linx gives him everything he wants (it's obvious that he's just scared of Linx). Bloodaxe says in awe, "Yours is a towering intellect, Irongron!"
- Pull the Thread: The Doctor, when he sees through Sarah Jane's cover story
- Scullery Maid: Sarah Jane poses as one to infiltrate Irongron's castle and drug the food.
- Slipping a Mickey: Sarah Jane drugs Irongron's men's food and drink.
- TechnobabbleSarah: I've never heard so much gobbledegook in my life, but I expect you know what you're talking about.
- Time Police: The Doctor finds himself in this role, and states that the Time Lords don't like "unauthorised" time travel. Well he should talk!
- Timey-Wimey Ball: The Doctor recognizes the Sontarans, complete with asking about their interminable war against Rutan Host, despite them never appearing in the series before. It's shown 12 years later that the Second Doctor had encountered them before, along with the Sixth Doctor.
- Title Sequence Replacement: Jon Pertwee's final season, showing him in a version similar to his successor's.
- Translation Convention: Both scientific technobabble and the Doctor's Quintessential British Gentleman slang are apparently interpreted into Norman French for Irongron.
- Unfortunate Names: Professor Rubeish's name sounds like "Rubbish". The Doctor almost thinks he's been insulted when the professor first introduces himself.
- Unwanted Rescue: When the Doctor finds Rubeish at the castle, the scientist doesn't want to be rescued because he's too interested in the work being carried out for Linx. Also, he's so nearsighted and so naive that he hasn't actually realized how much danger he's in.
- Wayback Trip/Giving Radio to the Romans: In this case, keeping firearms from developing centuries too early.
- Wham Episode: This episode names the Doctor's home planet, introduces one of the most popular companions of the series, Sarah Jane Smith, and also introduces recurring enemy race the Sontarans (although the Second Doctor will later have previously battled them). Along with a prototype version of the time-tunnel credits sequence, This episode is also the debut of the Diamond Logo, arguably the most recognizable logo from the classic series.
- What Happened to the Mouse?: We're introduced to the scullions who work in Irongron's castle, who get a significant scene discussing feminism with Sarah Jane. We see the Doctor go out of his way to evacuate Irongron's men, but we never see him go back for the women and they don't appear in later scenes. Sarah doesn't even express any concern about them. Did they get blown up?
- Where's the Fun in That?:
- After the Doctor tells the Brigadier that he'll go search for the missing Professor Rubeish in the TARDIS, he pretty much says this to the Brigadier after the Brigadier points out the TARDIS's not-quite-good landing record.The Doctor: A straight line may be the shortest distance between two points, but it is by no means the most interesting.
- The Doctor pretty much states his MO when Sarah Jane Smith asks "Are you serious?"The Doctor: About what I do, yes. Not necessarily about the way I do it.
- This is Irongron's reaction when he gets a firing squad of his men to kill the Doctor with their new rifles, and Linx tells him to let him (Linx) do it personally.Linx: Give me a weapon. I will destroy him.
Irongron: Come now, Linx. Would you spoil good sport?
- After the Doctor tells the Brigadier that he'll go search for the missing Professor Rubeish in the TARDIS, he pretty much says this to the Brigadier after the Brigadier points out the TARDIS's not-quite-good landing record.
- Worthy Opponent:
- Irongron briefly considers the Doctor as this, appreciating his wit as he dodges the bullets of the firing squad.Irongron: Beshrew me, I grow fond of this Doctor.
- Subverted with Irongron and Linx. They work to each other's mutual gain and occasionally exchange respect and good natured banter but in their time apart, they express entirely justified distrust and constantly plot to murder each other.
- Irongron briefly considers the Doctor as this, appreciating his wit as he dodges the bullets of the firing squad.
- Wrong Genre Savvy: See The Middle Ages above.
- Ye Olde Butcherede Englishe: When Sarah Jane starts speaking like this, Irongron's maid thinks she's nobility.