She presses the brass buzzer, and waits for the soldier to open the door. They stare at each other through the glass: a woman out of uniform, one knee spattered with what might be oil or viscera, hair matted at one temple with oil or soot from the deep underground and carrying a vandalised plastic doll’s house; opposite her, an impeccable armoured matriarch of some Arctic military service, permitted but not obviously carrying a firearm in the London area.