The Slitheen fight over their skin suits, hurriedly, as the people evacuate. The Sergeant fires into the air, and everybody starts running. He looks up at the sky, and the missile heading toward them.
Rose, the Doctor, and Harriet bundle into the cupboard. The crouch in a corner, the women on either side of him. "Nice knowing you both," says Harriet, and they all clasp hands. As they brace themselves, Harriet shouts, "Hannibal!" It's so cute and weird and off-the-cuff -- don't think for a second you'd come up with a better final shout -- that it kind of redeems the whole stupid "calcium" thing entirely. The Slitheen look up -- "Oh, bollo..." -- and the missile hits 10 Downing Street.
The building explodes in flames. I can't believe they just blew up the Prime Minister's residence. The heroes in the cupboard jostle about, and when it settles, the three of them step out into the smoking ruins. "Maiden Britain," breathes Harriet, who's proving to have quite a gift with the non-sequitur sentence fragments that somehow fit perfectly. The Sergeant hurries over to them, and Harriet -- duh -- flashes her ID at him: "Harriet Jones. MP, Flydale North. I want you to contact the UN immediately, tell the ambassadors the crisis is over and they can step down." She waves him off like a kid, adorably, and he gives in, just as adorably, with a simple "Yes, ma'am." Harriet grouses at the Doctor and Rose about how somebody's got to sort it all out, and remembers that they don't even have a PM anymore. The Doctor suggests that she herself have a go, and she laughs at him, once again calling herself a "back-bencher." Rose says she'd certainly vote for Harriet, who tells them to stop with this foolishness. They beam at her.
Harriet climbs across the wreckage toward a crowd, and the Doctor smiles at her, having finally placed the name. Harriet: "The Earth is safe! Sergeant!" She heads for the cameras and ambulances, and the Doctor spills: "Harriet Jones -- future Prime Minister. Elected for three successive terms: the architect of Britain's Golden Age." "The crisis has passed!" Harriet reports to the cameras. "Ladies and gentlemen! I have something to say to you all! Mankind stands tall, proud, and undefeated. God bless the human race!" The Doctor and Rose fondly watch Harriet taking flight, and turn and walk off quietly.
Jackie devours Rose, of course, and it's very sweet. They both close their eyes, back together again. The Doctor, chuffed indeed, starts up the TARDIS.