The child stands alone at Albion Hospital, and we zoom in: "Mummy?" Something has changed again. All the masks in the hospital climb out of their beds and make for the front door.
At the bomb site, the masks from closer in start to rattle the gates. The Doctor hurls orders: he tells Jack to secure the gates, and sends Rose and Nancy with his screwdriver to repair the hole Nancy made: "Setting 2428-D: reattaches barbed wire. Go!" That's funny. Jack slams the gate shut.
At Albion, the masks are marching as one from the front door, led by Dr. Constantine. Maybe he's like a Lieutenant Mummy? This story has more surrogate mothers than real ones. You have to look for the real ones.
Nancy helps Rose to sonic the fence back together, and asks what the deal is, causing Rose to fall back on the usual "you'd never believe me." But this is Nancy; she's got an answer for this handy: "You just told me that was an ambulance from another world. There are people running around with gas-mask heads, calling for their mummies, and the sky's full of Germans dropping bombs on me. Tell me: do you think there's anything left I couldn't believe?" Rose finds the one thing: "We're time travelers from the future." "What future?" Nancy asks, calling Rose mad. Rose looks up at the sky -- at the dirigibles and planes and explosions -- and her face goes soft: "Nancy, this isn't the end. I know how it looks, but it's not the end of the world or anyfing.... Listen to me. I was born in this city. I'm from here, in like, fifty years' time." Rose smiles at Nancy encouragingly: "I'm a Londoner. From your future." But Nancy wonders how that can be, since she's not German? Rose smiles hugely: "Nancy, the Germans don't come here. They don't win.... Don't tell anyone I told you so, but do you know what? You win." And how? The spirit of the Blitz. By becoming stronger than the thing that's coming. A mouse too small to fight can roar. Lions make the best mothers. Nancy laughs -- her mind blown -- and she and Rose run back to the Doctor and Captain Jack.
Captain Jack opens the hatch, still begging for his hands-off privileges: "It's empty. Look at it." The Doctor asks what he was expecting: "Bandages? Cough drops?" He turns to Rose, and she's like, "I dunno," but she does: the Doctor holds up a hand near his face. "Nanogenes!" she calls. "It wasn't empty, Captain," says the Doctor intensely. "There was enough nanogenes in there to rebuild a species." Jack goes gray. "...Getting it now, are we? When the ship crashes, the nanogenes escape. Billions upon billions of them, ready to fix all the cuts and bruises in the whole world. But what they find first is a dead child, probably killed earlier that night and wearing a gas mask." Rose can't believe that the nanogenes could bring them back to life, but the Doctor calls life just "nature's way of keeping meat fresh -- nothing to a nanogene." The ones in the transport, unlike Jack's, had never met a human being before, so they didn't know what it's supposed to look like. "All they've got to go on is one little body," the Doctor says, "and there's not a lot left. But they carry right on.Tthey do what they're programmed to do: they patch it up. Can't tell what's gas mask and what's skull, but they do their best. Then off they fly, off they go, work to be done.... Now, they think they know what people should look like -- and it's time to fix all the rest. And they won't ever stop. They won't ever, ever stop. The entire human race is gonna be torn down and rebuilt in the form of one terrified child looking for its mother, and nothing in the world can stop it!" That's...not so fictional, from where I'm standing. Jack protests that he didn't know, and the Doctor just looks at him coldly, and then goes to work with his screwdriver. Fixing the unfixable.
Nancy calls Rose to the perimeter, scared. The masks are getting closer, shambling over the rails of the traintracks. Rose comes running back, asking whether the ship is somehow summoning them. "It's calling up the troops. Standard protocol," the Doctor replies. But they're not troops, just Londoners in the Blitz. Just people. "This is a battlefield ambulance. The nanogenes don't just fix you up; they get you ready for the front line. Equip you, program you." Rose realizes that this is why Jamie can do all that stuff with the radios and the telekinesis. The Doctor: "...A fully equipped Chula warrior, yes. All that weapons tech in the hands of a hysterical four-year-old, looking for his mummy. And now there's an army of them." Weapons of mass reconstruction. They crowd the fence, and Jack asks why they aren't attacking -- they're waiting for the child? Nancy corrects him: "Jamie. Not 'the child.' Jamie." The Doctor looks at her and wonders.