"Martha, Donna. Donna, Martha. Please don't fight. I can't bear fighting."Paging the Doctor! When Martha gave the Doctor her old phone, this is the kind of situation she had in mind.Since he left, remarkable strides have been made in environmental engineering: in particular ATMOS, a gizmo installed in half the cars on Earth which neutralizes exhaust, with only the tiny side detail of being completely evil and a front for alien murders. ATMOS is the creation of a teenage genius by the name of Luke Rattigan, who is secretly working for the Sontarans, a warrior race of militaristic short guys who look a bit like potatoes. (Though the Doctor would like to remind you that to a Sontaran, you look like a shaved pink weasel-thing.)Martha and Donna are introduced and, to the Doctor's great relief, get on really well. Martha's now a proper doctor, and with UNIT. The Doctor's a little bit uncomfortable with how well she fits into a military organisation. She retorts that he's the one who got her the job in the first place. He wisely doesn't respond to that.The Doctor teams up with UNIT, but he doesn't like the way things have changed since the old days, and the reunion is an uneasy one. The Brigadier (now knighted) is a few continents away and unable to help out. Also, Martha is kidnapped by the Sontarans, and they create an evil clone of her.Meanwhile, Donna goes back home to get another earful from her mum, and to see Wilfred, her dear old grandad, again. The Doctor turns up to fetch her (and meets a delighted Wilfred and a highly apprehensive mum), just in time for all the ATMOS-equipped cars in the world to begin emitting clouds of poison gas! How can the Doctor stop an alien attack that's occurring in 400 million places at once?
— The Doctor
- Absence of Evidence: Donna is the first to find something legitimately suspicious at the factory:Donna: The first thing I noticed is an empty file.
The Doctor: Why, what's inside it? Or, what's not inside it?
Donna: Sick days. There aren't any. Hundreds of people working here and no one's sick. Not one hangover, man flu, sneaky little shopping trip, nothing. Not ever! They don't get ill.
- Affably Evil: Staal is as cordial as a Sontaran ever gets towards the two soldiers he meets, up until one of them starts with the height jokes.
- And Starring: Freema Agyeman is credited with an "And".
- Arc Words: Another reference to the Medusa Cascade.
- Artistic License – Gun Safety: The Sontarans use space magic to render ordinary firearms useless, and this is said to work by expanding the copper jackets of the bullets so that they can't leave the barrel. In reality, such a malfunction often causes the affected weapon to explode; the stuck bullet denies the burnt gunpowder gases any safe exit, so they exit unsafely instead by bursting the chamber or barrel. Fortunately for the UNIT troopers, in the episode it only results in the same click you'd get from a dry fire.
- Berserk Button: Don't say the Sontarans have a weakness, even if they actually do.
- Blue and Orange Morality: The 10th Doctor's notorious loathing of guns leaks into the people that carry them. He is snotty towards Colonel Mace, a Reasonable Authority Figure, also Russ, a Nice Guy grunt, because they carry guns. He says people that carry guns are usually bad guys, but Martha gives him an earful for this. The Brigadier, who the Doctor later wishes was involved in the situation, is the exception to this rule.
- Blunt Metaphors Trauma: Rattigan remarks that something is "cool" and Skool remarks "Is the temperature significant?"
- The Brigadier: Colonel Mace is a leading figure in UNIT which is a military organization in charge of Homeworld Security. He's a pretty nice guy. The trope namer himself doesn't appear — he's stuck in Peru.
- Broken Record: The factory worker Martha interviews only say "I am here to work" over and over.
- The Bus Came Back: Martha returns for a few episodes.
- Capture And Replicate: The Sontarans make a clone of Martha in order to infiltrate UNIT.
- Chekhov's Gun: Both the racketball in Luke's office and the rubber mallet used to whack the TARDIS console are used again to incapacitate Sontarans.
- Comically Missing the Point: Rattigan calls the Doctor "smarter than the average UNIT grunt". The Doctor gets upset and insists that he not call Ross, his escort, a grunt.
- Continuity Nod:
- To "Voyage of the Damned" (when Donna's grandfather met the Doctor) and "The Runaway Bride" (when Donna's mother met the Doctor).
- And "Dalek" (the "In-tru-da window" pun made by Henry van Statten).
- Donna's mother complaining about Donna disappearing for days.
- The Sontarans mention the Time War, and how the Doctor fought in it. They're upset because they weren't allowed to take part.
- Covered in Gunge: A creature in a pool of green slime.
- Cursed with Awesome: The Sontarans' armour has only one weak point, in the back of their necks. For the Sontarans, retreat is not only dishonourable, but impractical.
- Defeating the Undefeatable: Staal introduces himself as "Staal the Undefeated." The Doctor comments on the nickname's lack of foresight, pointing out that if he was defeated, he would have to be called "Staal the Not-Quite-So-Undefeated-Anymore-But-Never-Mind."
- Ditto Aliens: Staal and Skorr,them being clones, have only minor differences. Check Luke Rattigan's reaction when Skorr removes his helmet:Luke Rattigan: How... do you tell each other apart?
General Staal: We say the same of humans.
- Every Car Is a Pinto: Subverted when the ATMOS in the Land Rover suffers from the Logic Bomb, the Doctor and Ross Jenkins run for cover... then the sat nav system fizzles and sparks a little bit.The Doctor: [disappointed] Is that it?
- Exact Words: The ATMOS in the UNIT jeep was programmed to do precisely the opposite of what The Doctor tells it. So he tells it to drive into the river.
- Failed Attempt at Drama: Donna says she's going home. The Doctor gives her the big speech about everything he wanted to show her, how she's saved his life, how he was so very grateful for her company and... you're just popping home for a visit, aren't you? Also a stellar example of The Day the Music Lied.Donna: You dumbo. You great, big, outer space dunce.
- Fate Worse Than Death: A Sontaran would rather just shoot a person rather than brainwash them, because "Death has more honour".
- The ATMOS Sat Nav repeatedly saying "Turn Left".
- There's also the cloned copy of a person animated by the still-living person's memories.
- Fun with Acronyms: Both ATMOS and UNIT use the "using letters from within the words" method. Although it was somewhat enforced for UNIT — they didn't before, but then the UN started being much more sensitive about its name being used.
- Godwin's Law: Ross the UNIT soldier compares Rattigan's followers to Hitler's youth. It has dawn excercise and special diets and stuff.
- Grammar Nazi:
- The Doctor:Luke: If only that was possible.
The Doctor: If only that were possible. [glasses pull] Conditional clause.
- Later...Luke: You can't say "ATMOS system" 'cos it stands for Atmospheric Omission System. So you're saying, "Atmospheric Omission System System." Do you see, Mr. Conditional Clause?
- The Doctor:
- Guns Are Useless: The Sontarans' Applied Phlebotinum prevents guns from being fired in their presence. Techno Babble explains that it's because of the bullets' copper jackets.
- Hollywood Spelling: "If you're gonna go to print, spell my name right. Rattigan, with two ts."
- I Can't Feel My Legs: Staal's Boom Stick shoots paralyzing beam.
- Idiot Ball:
- At the start of the episode Jo Nakashima is protesting at how dangerous cars with Atmos are, and then proceeds to get into one.
- UNIT has all their vehicles fitted with ATMOS when they suspect there's something wrong with it. Ross is kind enough to lampshade this when The Doctor asks. They can't get rid of them until they have proof.
- Martha walks into a secluded area with a couple of grunts that only ask for her security clearance before escorting her away. This is after she suspects hypnotism and is going to talk with Colonel Mace. You'd thinking traveling with The Doctor would make her more Genre Savvy.
- Insufferable Genius: Luke Rattigan doesn't like it when someone out-geniuses him. See Grammar Nazi for just one example of it.
- Insult Misfire: Don't call Ross a grunt.
- Just One Second Out of Sync: The ATMOS has a "temporal pocket" containing the gas emitter.
- Magical Computer: The ATMOS reduces emissions and works as a sat-nav system. Also, it can completely take over your car.
- The Missus and the Ex: Subverted; the Doctor attempts to head this off, only for Donna and Martha to jump straight to making fun of him. "Oh, I'd rather you were fighting."
- Names to Run Away from Really Fast: Skorr the Bloodbringer.
- No One Could Survive That: Largely averted. The Sontarans initially think the Doctor is dead, but when they get proof that he's not, they accept it without question. Of course, they know the Doctor, so obviously they'd know how hard it is to kill him.
- Proud Warrior Race Guy: All the Sontarans talk about the "delight of battle" and how a "good soldier" joins the tray personally. The Doctor points out that hiding and stopping bullets are very unlike them. "A sontaran faces bullets with dignity. Shame on you!"
- Pun: "We have an intruder." The Doctor responds with: "How did he get in? In-tru-da window?" referring back to "Dalek".
- Reality Ensues: Sorry, Doctor. Not every Logic Bomb results in an explosion; just the system shorting out.
- Real Life Writes the Plot: The exploding ATMOS was supposed to be a more impressive faire, but it would've been too expensive to blow up the Rover (and the Army wouldn't like it, either), so it was rewritten to have the ATMOS controller give a few sparks. It also fulfills the Rule of Funny.
- Red Baron: General Staal the Undefeated and Commander Skorr the Bloodbringer. The Doctor mocks the former thoroughly.
- Red Shirt: Red Berets, in this case; the UNIT soldiers are easily-killed foot soldiers for the good guys.
- Scheherezade Gambit: On meeting Staal, the Doctor immediately reveals he knows what a Sontaran is, discouraging Staal from just killing him on the spot.
- Spoiled Brat: The Doctor's opinion of Rattigan.Doctor: It's been a long time since someone said 'no' to you, isn't it?
- Stuff Blowing Up: The Doctor's disappointed when Every Car Is a Pinto doesn't happen.
- Take That: To The '80s in one way or another.note The Doctor: Getting a little too close to the 1980s.
Donna: What am I gonna do, put a dent in them?
The Doctor: Well, someone did.
- Teen Genius: Luke Rattigan is a teenager with an IQ "rated at 174."
- The Easy Way or the Hard Way: The soon-to-be-brainwashed UNIT soldiers tell the already brainwashed factory workers of their options.
- What the Hell, Hero?: Martha, who's grown to know and like Colonel Mace, calls out the Doctor for his attitude towards Mace.
- Where's the Kaboom?: After the UNIT jeep fails to explode at all. "Is that it?"