History Recap / DoctorWhoS30E5ThePoisonSky

* MythologyGag: In New York, one of the buildings has a name reading "Butler Institute". The Butler Institute was a sinister EnigmaticInstitute in the Literature/VirginNewAdventures book ''Cat's Cradle: Warhead''.

* CloningBlues: Martha's clone quickly falls into a downward spiral of it when Real!Martha's awakening cuts off her life support.

** The Doctor mentions Captain Jack to Martha's clone.

The one where the Doctor has an in-joke with himself and Martha has a clone with a bald spot.

* ShutUpKirk: A rare heroic example: "Thank you, Doctor, for your lack of faith, but unfortunately I've stopped listening." After two episodes of contempt and insults from the Doctor, whom he had treated with utter respect from the start, Colonel Mace finally stops listening and proceeds to prove the Doctor wrong and wipe the floor with the so-called "universe's greatest soldiers". However, the mothership would have wiped them out from space if it wasn't for a mixture of the Sontarans being {{Blood Knight}}s and wanting to have fun on the ground, and the Doctor, so he was correct about them standing no chance against the Sontarans. Notably, while the Doctor never congratulates Mace on the bullets thing (though this being the Doctor he wouldn't) he flat-out congratulates Mace for the use of the ''Valiant'', being genuinely impressed.

* AuthorityEqualsAsskicking: Colonel Mace can kill a Sontaran — Commander Skorr, no less, who's an example in his own right — in one shot ''without'' using the back of the neck weakness. No one else can do this. Oh, and he warns the Sontaran of his presence.
-->"You will face me, sir!"

* ColonelBadass: Colonel Mace proves he's one not only by inspiring UNIT to put some steel-jacketed rounds in Sontaran heads, but he also double-taps Commander Skorr with a pistol — this after [[AsskickingEqualsAuthority Skorr]] easily took down two UNIT soldiers armed with automatic rifles, and Mace intentionally sacrifices the advantage of coming up behind him to look him in the eye.

** Mace challenging [[AsskickingEqualsAuthority Commander Skorr]] rather than just double-tapping him from behind. Since Mace is a ColonelBadass, he still puts Skorr down.

* AnAxeToGrind: When the Doctor and Donna are unable to free Wilfred from his car, Sylvia comes along with an axe and smashes the windscreen. She claims she has it in case of burglars.

** However, this doesn't stop them having an OhCrap moment when Luke replaces the Doctor — because they know that unlike the Doctor, he won't hesitate.

* FreezeFrameBonus: Rose Tyler can briefly be seen on the TARDIS's screen, yelling the Doctor's name, before it switches to the UNIT control room.

* RedshirtArmy: {{Zigzagged}} with the UNIT troops. Initially the Sontarans slaughter them with their [[EnergyWeapon laser guns]], because the troops are defenseless against them as the Sontarans' "[[Technobabble Cordolaine Signal]]" renders UNIT's firearms inoperable. As soon as Mace is informed of the bullet issues, they switch ammunition to steel casing bullets (which avoids the problem of copper bullet expansion blocking the barrel), after which, they then goes back in and they mop the floor with them, meaning the Sontarans become this.

* ArmourIsUseless: The Sontarans' armour, despite clearly looking bulkier than the standard UNIT armour, seems to be mostly decorative, as UNIT soldiers mow the Sontarans down when their firearms gain steel-cased bullets to avoid the Cordolaine signal. It might be that it's specifically designed to counter ''energy'' weapons, such as laser guns, in much the same way that Kevlar is specifically designed to stop bullets, not bladed weapons, such as blades.

** "[[Recap/DoctorWhoS27E9TheEmptyChild Are you my mummy?]]"

Rose very, very briefly shows up on a UNIT screen, screaming at the Doctor. He doesn't notice.

* ApocalypseHow: The Sontarans' AtmosphereAbuse threatens to at least cause a ApocalypseHow/Class2 that would presumably force humanity to exist in sealed environments (until the Sontarans eradicate these straggler pests from their new clone world), and more than likely would actually cause a ApocalypseHow/Class5 for Earth's native life while the Sontarans can come in and convert the planet's landscape into a breeding planet for themselves in the aftermath.
* ArmourIsUseless: The Sontarans' armour seems mostly decorative, as UNIT mows them down when their firearms are working again. It might be that it's specifically designed to counter energy weapons, the same way that Kevlar is specifically designed to stop bullets, and less good against more primitive weapons like blades. Also, given how much experience UNIT has with aliens, it's also probable those aren't regular bullets.
* ArtisticLicenseGunSafety: The Doctor throwing Luke's gun across the room is ''incredibly'' dangerous. [[FridgeBrilliance That is, assuming the gun is even loaded.]][[invoked]]

* CloningBlues: Clone!Martha quickly falls into a downward spiral of it when Real!Martha's awakening cuts off her life support.

* HyperAwareness: The Doctor can tell that clone!Martha is a clone because of "reduced iris contraction", and a "thinning of the hair follicles on the left temple".

* TheNoseKnows: Clone!Martha apparently smells bad, but only the Doctor can tell.

* OutGambitted: The clone!Martha prevents UNIT from launching nuclear weapons at the Sontarans, only to discover that's just what the Doctor wanted, having immediately recognized her as a fake.
* OutOfCharacterAlert: Clone!Martha has the original's memories, but not her concern for her family. She also misses the Doctor going "Avanti" instead of "allons-y", and gives off several other tells to an alien with HyperAwareness.

* RedemptionEqualsDeath: Luke Rattigan [[HeroicSacrifice commits suicide, saves the Doctor, and destroys the aliens]] when he realizes how badly he screwed up.
* RedshirtArmy: {{Subverted}} with the UNIT troops. Initially the Sontarans slaughter them with their [[EnergyWeapon Frickin' Laser Beams]] because they've used {{Technobabble}} to render UNIT's firearms inoperable. But UNIT just pulls out, switches ammunition, then goes back in and mops the floor with them.

* InsufferableGenius: Luke Rattigan is revealed to be a JerkassWoobie because of this. All he ever really wanted was to have some real friends who would praise him for his achievements, hence why he was so willing to work for the Sontarans, even hoping they'd adopt him into the fold, as it were. When they reveal he's disposable, he takes the Doctor's comment that he should do something clever with his life to its logical conclusion and decides to atone for his error by doing a TakingYouWithMe to the Sontaran mothership.

* ArmourIsUseless: The Sontarans' armour seems mostly decorative, as UNIT mows them down when their firearms are working again. It might be that it's specifically designed to counter energy weapons, the same way that Kevlar is specifically designed to stop bullets, and less good against more primitive weapons like blades.

** The whole Brig-stranded-in-Peru thing harkens back to the classic run and ''Series/TheSarahJaneAdventures'', where it's a RunningGag for the Brig to be "stranded in Peru" when important things are happening with UNIT.

* {{Squick}}: InUniverse, as disgusted as Rattigan's fellow students are by his plan to destroy the Earth and move the school off-planet, what ends up making them leave is that he planned a ''[[GeniusBreedingAct mating program]]'' for them. (What's worse is that you'd need about 200 people to repopulate humanity without a ''lot'' of incest, and there are nowhere ''near'' 200 students at Rattigan's academy.)

* TemptingFate: Martha really should have said her goodbyes and "I'm good here" stuff ''outside'' the TARDIS.

* BizarreAlienSenses: The Doctor can tell that clone!Martha is a clone because of "reduced iris contraction", and a "thinning of the hair follicles on the left temple".

-->'''The Doctor''': (enters the Rattigan Academy via transport, Donna and Martha in tow) Here. The Rattigan Academy, owned by-
-->(Luke enters, aiming a gun)
-->'''Luke''': (nervous) Don't tell anyone what I did. It wasn't my fault, the Sontarans lied to me, they-
-->'''The Doctor''': ([[NoSell walks past Luke while taking his gun;]] infuriated) ''If I see one more gun...'' (tosses gun away)

* SoldierVsWarrior: UNIT fights like soldiers in organized squads, the Sontarans fight like individual warriors — and UNIT are much more mobile. The Sontarans didn't stand a chance.

* TwinThreesomeFantasy: Discussed; the Doctor tells the Martha clone that she'd best not wear a T-shirt saying "Clone" in front of Captain Jack Harkness.

* UnwittingPawn: The Martha clone doesn't realize that the Doctor rumbled her a good while ago, but like the Sontarans he ''also'' wants her to keep cancelling the weapons launch. Furthermore, he deliberately tells Mace that he's going to use the TARDIS to get onboard the Sontaran ship within Clone Martha's hearing, leading her to have the TARDIS teleported to the ship with Donna onboard, unbeknownst to her.

* UnwittingPawn: The Martha clone doesn't realize that the Doctor rumbled her a good while ago, but like the Sontarans he ''also'' wants her to keep cancelling the weapons launch.

* FamousLastWords:
** "[[SincerityMode Wonderful]]..."
** "Sontar. HAH!"

* InformedAbility: The Sontarans being the "universe's greatest soldiers" when their tactics appear to mostly consist of walking forward and shooting people. Sure they mopped the floor with the UNIT forces in the first encounter, but once the humans got past the Sontarans' ''blatant cheating'' (a field which prevented their weapons from firing, making them incapable of even fighting back) they absolutely [[CurbStompBattle curb-stomped]] the "invincible" Sontarans. And unlike, say, Daleks with powerful shields, these guys get cut down by bullets pretty easily when their copper-expanding gimmick fails.