"You might as well have worn a T-shirt saying 'clone'.... Although, maybe not in front of Captain Jack."So the world's going to shit with Sontaran cloning gas spewing out of every car on the planet. UNIT gives the Doctor a gas mask (and ignores him when he quips "Are you my mummy?"). He hangs out with obvious-clone-Martha for a bit, because even though she's working for the Sontarans she happens to be doing exactly what he wants her to do: stop UNIT from launching a nuclear attack.Rose very, very briefly shows up on a UNIT screen, screaming at the Doctor. He doesn't notice.Luckily, the Doctor can whip up something that can burn all the gas, cleansing the air, using technology that has conveniently been developed by Rattigan's geniuses for when they were going to move to a new planet. He also, once again, decides to sacrifice himself, but Rattigan takes his place and, in an Heroic Sacrifice, blows up the whole Sontaran fleet with a Sontar-HA!As the Doctor and Donna prepare to see Martha off, the TARDIS is involuntarily pulled away in time, to an unknown destination...The white Flesh cloning technique will become important again in series 6.
— The Doctor
- An Axe to Grind: When the Doctor and Donna are unable to free Wilfred from his car, Sylvia comes along with an axe and smashed the window open. She claims she has it in case of burglars.
- Anger Born of Worry: After the Doctor's near-sacrifice, Martha immediately hugs him. Donna whacks him on the arm, then hugs him.
- Armor Is Useless: The Sontaran's armor seems mostly decorative, as UNIT mows them down when their firearms are working again.
- Atmosphere Abuse: The Doctor sets it on fire!
- Atomic Hate: No Russia, for some reason. Even though North Korea gets in on the action!
- Authority Equals Asskicking: Colonel Mace can kill a sontaran with one shot without using the back of the neck weakness. No one else can do this.
- Badass Army:
- Subverted. The Sontarans appear to be one of these until UNIT overcomes their weapons being disabled and gives them the ass-kicking of the century. The Doctor had just introduced them as the greatest soldiers in the universe, too. Despite all their talk of discipline they fought as individual warriors, and once their advanced technology (a field that made copper-jacketed bullets unfireable) was got around, they were immediately cut down by UNIT's organized fire-teams. It's stated that they could have easily destroyed Earth from orbit without much trouble, but on the ground UNIT was more than equal to the challenge, especially since the Sontarans weren't expecting any resistance and allowed themselves to be caught off-guard.
- Played straight with UNIT, as once they find a way around the Sontaran's anti-gun field they proceed to mow down the Sontarans with ease.
- Big Damn Gunship: The USS Valiant, making a return appearance, accompanied by the necessary Rousing Speech.
- Blue and Orange Morality: Commander Skorr seems genuinely pleased that Colonel Mace had the honour to demand he turn around before putting a few bullets into him, and compliments him on his martial virtue as he lays on the ground, dying.
- The Brigadier:
- Mace again carries on from the previous episode.
- Sir Lethbridge-Stewart himself also gets a Shout-Out. The Doctor says that he wishes "The Brigadier" was here. Mace agrees, compliments him and says that he's "stranded in Peru".
- Chekhov's Gun: Chekhov's Hammer in this case as Donna uses the one the Doctor occasionally uses on the TARDIS console.
- Cloning Blues: Clone!Martha quickly falls into a downward spiral of it when real!Martha's awakening cuts off her life support.
- Colonel Badass: 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.Colonel Mace: You will face me, sir!
- Continuity Nod:
- "Are you my mummy?"
- The Valiant from the end of series 3.
- Torchwood's Sunrider weapon from "The Christmas Invasion".
- The Doctor, who Donna can see and hear on a monitor, secretly communicates with her the same way he did with Mickey in a previous episode. He gets her attention by saying "noble", while with Mickey he repeatedly used the word "idiot" (which is what he frequently called him).
- The whole Brig-stranded-in-Peru thing harkens back to the classic run and The Sarah Jane Adventures, where it's a Running Gag for the Brig to be "stranded in Peru" when important things are happening with UNIT.
- Curb-Stomp Battle: The Sontarans find themselves on the receiving end of one this time once UNIT figures the Sontaran technology that stops their guns from firing. Once that happens, the aliens start getting mowed down.
- Cutting the Knot: While Donna and the Doctor try to fiddle with the car to unlock it, Donna's mother comes over and smashes the windscreen with an axe.
- Deadpan Snarker: Colonel Mace learns this (not saluting) is the best way to cope with the Doctor's constant snide comments.
- Deadly Gas: Downplayed - the gas is harmful, but not fatal until it reaches a very high density. This is a hint that it's not meant to be a weapon, but something else.
- Defcon Five: Averted, the DEFCON status is used correctly. Nukes are ordered to be launched at Defcon 1.
- Doesn't Like Guns: The Doctor snatches Luke's gun out of his hand and throws it away without breaking his stride. "If I see one more gun..."
- Don't Make Me Destroy You: The Doctor puts his own life at risk to give the Sontarans a chance to walk away. They're far too egocentric to surrender and decide it'll be worth it if he gets blown up with them.
- Enemy Mine: The united nuclear response includes India, Pakistan, the USA, China and North Korea. (Oddly, not Russia.)
- Famous Last Words:
- Skorr: "Wonderful".
- "Sontar. HAH!"
- Failed Attempt at Drama: The Doctor gives Donna her own TARDIS key, echoing Rose and Martha. "Quite a big moment, really." Donna suggests they celebrate after dealing with the poison gas.
- Fate Worse Than Death: Luke's fellow students clearly consider his proposed "utopia" to be this; not even threatening them at gunpoint gets them to sign on.Luke: I designed a mating program. I planned the whole thing!
Student: Well then, shoot me. (she leaves, as do the others)
- Brilliant but unnoticeable:Donna: (to Martha, who wears the Doctor's coat over her hospital-type gown) You know, that coat, sort of works.
Martha: Feel like a kid in my dad's clothes.
Donna: Oh, well if you're calling him dad you’re definitely getting over him.
- For a fraction of a second, Rose Tyler appears on the screen of the TARDIS when the Doctor sends his message to the Sontarans.
- Brilliant but unnoticeable:
- Fun with Acronyms: Taken to its logical conclusion with ATMOS, which stands for "Atmospheric Omissions System". The final S has to come from System, or Rattigan's whining makes no sense. One would think "omissions" is a misspelling of "emissions", but it's actually a pun: the system takes the dangerous chemicals out of the car's emissions; it's an emission omission system. That's just the kind of joke somebody like Rattigan would think was clever.
- Gas Mask, Longcoat: The Doctor puts on a gas mask while his coat is on.
- Genius Breeding Act: Luke tells his fellow Teen Geniuses about the one he has planned. They don't respond enthusiastically.
- Glory Seeker: The Sontarans would rather get blown up than let the Doctor win. In fact, getting blown up with the Doctor is even better! What a glorious death that would be!
- Gunship Rescue: "UNIT carrier ship Valiant reporting for duty, Doctor."
- Heel–Face Turn: Rattigan rescues The Doctor from his own Heroic Suicide so he can finish off the Sontarans himself.
- He Had a Name: "He wasn't "Greyhound 40", his name was Ross. Now listen to me, and GET THEM OUT OF THERE!"
- Heroic Sacrifice: Luke "does something clever" by swapping himself with The Doctor and blowing up the Sontarans and himself.Luke:Sontar-HA!
- Honor Before Reason:Martha: Just send that thing up on its own. I don't know, put it on a delay.
The Doctor: I can't.
Donna: Why not?
The Doctor: I've gotta give them a choice.
- Hostile Terraforming: Weakened by their eternal war with another race of Scary Dogmatic Aliens, the Sontarans hatched an uncharacteristically circuitous plan to bathe the earth in gas which is poisonous to native life but nutritious to themselves, so that they can use it to spawn more soldiers.
- Humanity Ensues: The clone-Martha gives the real Martha some vital information after considering her fake memories while she dies.
- Idiot Ball: Donna. Possibly justified because she is alone in a dangerous situation (and thus may not be thinking as clearly).Donna: (on phone to the Doctor, regarding the use of a door switch) But it's Sontaran-shaped, you need three fingers!
The Doctor: ...You've got three fingers.
Donna: Oh yeah!
- Despite knowing about the Sontaran's gun-blocking signal, neither the Doctor or Ross tell the Colonel, resulting in Ross's untimely demise.
- Informed Ability: 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 Sontaran's blatant cheating (a field which prevented their weapons from firing, making them incapable of even fighting back) they absolutely 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.
Considering this was coming from a Technical Pacifist who views the word "soldier" as an insult and that Sontarans are obviously a Martyrdom Culture that believes War Is Glorious this actually may have been a bit of Fridge Brilliance. And it was stated several times throughout the episode that the Sontarans were holding back since they could have killed everyone easily, but needed the planet intact and the Sontarans inside the factory were caught flat-footed since they expected no resistance since the solders' weapons were disabled.
- Continuity Nod: When UNIT begins passing out gas masks, the Doctor dons his and asks the Colonel in charge "Are you my mummy?"
- In the Back: Colonel Mace defies it, but only just. Coming up behind Commander Skorr during the UNIT counterattack, he bellows, "You will face me, sir!" and then puts three bullets in Skorr's chest the second he turns around.
- Insufferable Genius: Luke Rattigan is revealed to be a Jerkass Woobie for why. 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 with his life to its logical conclusion and decides to atone for his error by doing a Taking You with Me to the Sontaran mothership.
- It Has Been an Honor: "Donna, thank you. For everything. Martha, you too. Oh, so many times. Luke, do something clever with your life."
- Just Between You and Me: Defied: "A general would be unwise to reveal his strategy to the opposing party."
- Kick the Dog: When Donna and Sylvia talk on the phone, Donna tries to reassure her mother that people are working on the gas problem. Sylvia just snidely asks how she'd know that.
- Leaning on the Fourth Wall: When the Doctor complains about being stuck on Earth like a human, he quickly apologizes. As he does that, he looks at the camera for long enough that this apology is more to the viewers than Martha.
- Martyrdom Culture: The Sontarans.Doctor: General Staal, you know what this is. But there's one more option: you can go. Just leave. Sontaran High Command need never know what happened here.
Staal: Your stratagem would be wise if Sontarans feared death, but we do not.
- Mauve Shirt: After spending 1.5 episodes as The Doctor's sidekick Ross Jenkins is killed in battle. This is why The Doctor doesn't like guns!
- Monumental Damage: Though they aren't damaged, news reports show poison gas around the Hagia Sophia and the Sydney Opera House. Also, the ignition of the gas in the atmosphere sweeps over the Chrysler Building in New York.
- Mythology Gag: Rattigan calls the planet he intends to colonize "Earth.2", similarly to how the Cybermen referred to themselves as "Human.2".
- Not Herself: Martha. The Doctor suspects this almost immediately — one of the first things he asks the clone is if she's called her family. "No, what for?" Also, she smells.
- Oh Crap!: The Sontarans, when they see that Rattigan has replaced the Doctor.
- Out-Gambitted: The clone-Martha prevented UNIT from launching nuclear weapons at the Sontarans, only to discover that was just what the Doctor wanted, having immediately recognised her as a fake.
- Proud Warrior Race Guy:Skorr: (dying) Wonderful...
- Real Person Cameo: Newsreader and presenter Kirsty Wark.
- Red Sky, Take Warning: This one is burning with a global fire.
- Redemption Equals Death: Luke Rattigan commits suicide, saves the Doctor, and destroys the aliens when he realizes how badly he screwed up.
- Redshirt Army: Subverted with the UNIT troops. Initially the Sontarans slaughter them with their 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.
- Rousing Speech:
- Mace gives one to his soldiers about how they're going show the aliens that they are not puny earthlings. The mocking laughter stops now! The result is a highly motivated fighting force.
- Rattigan's gives one to his Academy geniuses about how Earth doesn't appreciate them and how they can leave it behind to start again! The result is everyone walking out on him.
- Squick: In-universe, 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 breeding 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.)
- Shut Up, Kirk!: 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 the Doctor, so he was correct about them standing no chance against the Sontarans.
- Stuff Blowing Up: The Doctor lights the upper atmosphere on fire. If the crossed fingers and "Please, please..." muttering are any indicator, the Doctor wasn't sure it wouldn't destroy the Earth.
- Taking You with Me: The Sontarans consider their deaths acceptable if they get to take the Doctor down with them. They have five seconds to reconsider when Luke takes his place.Doctor: You'll die, Staal!Staal: Knowing you die too.
- Talking to Herself: Martha talks to her clone; she even calls her Martha.
- Tempting Fate: Martha really should have said her goodbyes and "I'm good here" stuff outside the TARDIS.
- World-Healing Wave: Setting the sky on fire to remove the poison.
- You Are Better Than You Think You Are: The Doctor to Donna when she thinks she can't be helpful.
- You Have Outlived Your Usefulness: The Sontarans execute the brainwashed human soldiers, and were planning to use Luke and his students as target practice.