->'''Harrison Chase''': "What do you do for an encore, Doctor?"
->'''The Doctor''': "I win."
->''"You and your kind are nothing but parasites. You're dependent upon us for the air you breathe and the food you eat. We have only one use for you..."''
->-- '''The Krynoid''', speaking through Harrison Chase
The TARDIS arrives in England as two large alien seed-pods are found in the Antarctic permafrost. Helicoptered out to the Antarctic base to see for himself, the Doctor identifies them as Krynoids: a particularly rapacious plant that will, if allowed to germinate, consume all life on Earth.
One of the scientists, Winlett, is infected by the pod and begins to turn into a Krynoid himself. But he's destroyed by a bomb set by a mercenary, Scorby, and a rather confused botanist, Keeler, who steal the other pod on behalf of their employer, plant collector (and nutjob) Harrison Chase. Chase takes Sarah hostage and plans to open the pod in her presence, which will infect her. The Doctor rescues Sarah, and Keeler, who genuinely never wanted to get caught up in a murder case, ends up infected. This doesn't bother Chase much, and he begins to feed Keeler raw meat to accelerate the transformation. At this point, people start calling UNIT, but the Brig is in Geneva and his replacement isn't really the quick type.
The Keelernoid grows bigger and bigger, eventually beginning to take over Chase's mansion, while the mad collector decides to turn the Doctor into compost to feed it. But he ends up falling into the crusher himself, while the Krynoid is bombed by [[UltimateDefenceOfTheRealm the RAF]].
Not to be confused with "[[Recap/DoctorWhoS6E5TheSeedsOfDeath The Seeds of Death]]".
* ArtShift: Third of four Tom Baker stories which use video rather than film for location shooting; as with "[[Recap/DoctorWhoS12E1Robot Robot]]", this was to accommodate the visual effects used in Parts 5 and 6.
* BBCQuarry: As Antarctica with a white paint job. A different part of the same quarry was then used as an actual quarry for the fight scene between the Doctor and Chase's chauffeur.
* BodyHorror: There's no other way to describe the Krynoid transformation.
* BondVillainStupidity: Scorby, '''all the time'''.
* ConveyorBeltODoom: Leading into Chase's compost machine.
* DressingAsTheEnemy: The Doctor gains entry to Chase's mansion by stealing the hat and coat of the limo driver who tried to kill him and just driving through the front gate. Once he actually gets ''out'' of the car and the guards realize he's not the regular driver, the disguise fails. HilarityEnsues.
* TheExtremistWasRight: Scorby suggests bombing the Krynoid at one point but the Doctor shoots him down, saying that nothing they have to hand would create a powerful enough explosion. Cut to a few episodes later, and the RAF provides just such an explosion.
* FateWorseThanDeath: "It's more serious than death, Mr. Stevenson. He's [[BodyHorror changing form]]."
* ForScience: Chase's original motivation until the Krynoids possessed him.
* FrickinLaserBeams: UNIT now has rather clunky and homemade-looking laser guns. It still does little more than annoy.
* GardenOfEvil: Chase's estate is turned into one of these as all the flora falls under the control of the Krynoid.
* HoistByHisOwnPetard: Chase falls victim to the [[ConveyorBeltODoom compost machine]], which he'd used earlier as a murder weapon.
* IKnowYoureInThereSomewhereFight: Averted by the first Krynoid, as the Doctor makes it clear that Winlett's consciousness was destroyed at a relatively early stage of the infection. Subverted by the second Krynoid, as it's revealed that the Krynoid ''did'' keep some of Keeler's personality... but only enough to enable it to speak English.
* ImmuneToBullets: Averted; for once the Doctor recommends dealing with a menace via military means... and the Brigadier isn't there to see it.
* InsistentTerminology: After Winlett fully transforms into an early-stage Krynoid, the Doctor flips out whenever anyone refers to it as "Winlett" rather than "the Krynoid," likely because of the danger of someone hesitating to kill the Krynoid in the vain hope that Winlett can somehow be restored.
* KarmicDeath: Chase ends up shredded in his own human compost machine, after trying to drag the Doctor in. ''While the Doctor was trying to save him''.
* KillUsBoth: The Doctor ends the story by calling in an air strike on a building he's trapped in, due to the danger of the Krynoid releasing its seeds all over the planet. He gets out in time.
--> '''Scorby:''' Get your hands up. Turn around, Doctor.\\
(The Doctor does a full 360 turn.)\\
'''Scorby:''' Facing ''this way.''\\
'''The Doctor:''' Have we annoyed you or something?\\
'''Scorby:''' Shut up. Okay, start talking.\\
'''The Doctor:''' Wolfgang Amadeus Mozart had perfect pitch--
-->'''Scorby:''' What happened to him?
-->'''The Doctor:''' Who, Wolfgang Amadeus? (looks at the corpse next to him) ...Oh, ''him''! Oh, he died.
* LittleOldLadyInvestigates: Amelia Ducat, quite awesomely so.
* ManEatingPlant: As the Doctor notes in the first episode, on planets where the Krynoid gets established, the vegetation eats the animals.
* MinionWithAnFInEvil: Keeler is only a botanist, sure, but you'd think Chase would've sent someone more ruthless to assist Scorby in Antarctica. Keeler objects to everything Scorby does and even initially refuses to use a gun. When he finally accepts a gun the poor guy is such a nervous wreck it's amazing he doesn't accidentally shoot himself.
* MolotovCocktail: Scorby makes one to fight the Krynoid. This scene earned the wrath of the MoralGuardians (see below).
* MoralGuardians: One of a number of Who stories from the era to be specifically attacked by Mary Whitehouse. In this case, she complained about "strangulation by obscene vegetable matter" and the possibility of children imitating the scene where Scorby makes a petrol bomb.
* NeckSnap: The Doctor [[FamilyUnfriendlyViolence notoriously]] appears to do this to an anonymous security guard at one point, although it appears to have been non-fatal.
* ObstructiveBureaucrat: The Doctor demonstrates how to get their co-operation.
-->"If that Krynoid spawns it will mean the end of everything, even your pension!"
* OpenHeartDentistry: When one of the staff of the Antarctic research station needs an alien-Virus-infected limb amputated, a biologist is tasked to perform the emergency surgery because he's a better choice than the geologist or botanist: at least he's probably held a scalpel before, if only for dissections.
* PutOnABus: This serial marked the last appearance of UNIT in the series for a long time. Except for a minor appearance in ''[[Recap/DoctorWho20thASTheFiveDoctors The Five Doctors]]'', there wouldn't be another UNIT story until ''[[Recap/DoctorWhoS26E1Battlefield Battlefield]]'' 13 years later.
* PragmaticVillainy: When Amelia, who Chase tried to welsh on earlier, comes around demanding her money for the painting she did, Chase not only pays what he owes but ''doubles it'' in order to get her out of his house as quickly as possible. See also RewardedAsATraitorDeserves below.
* PrivateMilitaryContractors: Scorby. Chase's house is also guarded by his private security force armed with Uzis.
* RecycledScript: Noticeably recycled from an episode of ''Series/TheAvengers'' (not by the same writer). Also strong similarities to ''Series/TheQuatermassExperiment''.
* RedemptionEqualsDeath: Dunbar.
* RewardedAsATraitorDeserves: Completely averted. Chase actually pays Dunbar, his spy in the World Ecology Bureau, the briefcase full of money he promised him rather than killing him.
* SaveTheVillain: The Doctor tries to save Chase, who responds by trying to pull him into the compost machine with him. Big mistake, as it's difficult to hold onto someone while your legs are being crushed.
* ScrewThisImOuttaHere: Most of Chase's guards wisely bail offscreen when things start getting rough, except for one who apparently wasn't fast enough and gets killed by some vines.
* [[SelfDisposingVillain Self-Disposing Villain]]: See the Save The Villain example above.
* SissyVillain: Chase: "I could play all day in my green cathedral!"
* SmugSnake: Chase is ''unbelievably'' punchable.
* StuffBlowingUp: Yet another grand old British manor bites the dust in the last episode.
* StylisticSuck: Chase's music.
* SuperWindowJump: The Doctor diving through the skylight to rescue Sarah.
* SuspiciouslySimilarSubstitute: Two this time: Sergeant Henderson for Benton and Major Beresford for TheBrigadier.
* TapOnTheHead: Chase knocks Henderson out by bopping him lightly with a big wrench.
* UtopiaJustifiesTheMeans: The Krynoid seems to have this as an instinct. Chase likewise feels this way when it comes to plants.
* WasOnceAMan: Winlett, then Keeler.