But the episode as aired, and God knows how much even less sense the US version made, has already made such a hash of this lady that it doesn't really matter anymore that all her lines are just that, one-liner smart-assiness that isn't even all that fresh and manages to make the exact opposite point it's trying to make: "The Cybermen offered me the one thing I wanted: liberation!" Which ends up being like, feminists are not only incomplete men, but also fucking crazy bitches, which is not the intention, but then, purposely leaving out all possible motivation for a character's actions tends to have that effect.
So whatever, the Doctor notifies the Cybermen that he's the real Doctor, proving it with an infostamp, and asks what the kids are all about. "What are children ever needed for? They're a workforce," Mercy explains. "Very soon now, the whole Empire will see. And they will bow down, in worship... The perfect day for a birth, with a new message for the people." What that message actually will be we don't know and never will, because she starts tripping balls well before that time, but I mean, at that point you'd be stupid to care what her plan is, because giant robots are awesomer than any amount of well-written TV.
The Cybermen beat on their tin chests and step forward to kill the doctor and Rosita, but then Jackson Lake shows up, having strapped the bandolier of infostamps across his chest and zapping Cybermen willy-nilly. Maybe it's his new coping mechanism; it certainly looks therapeutic. Mercy screams for backup -- "Shades! Shades!" -- and Rosita makes the time to punch her in the face for some cathartic reason, so then she rolls around with the Cybermen awkwardly and the Doctor and Rosita are smug, and when Mercy stands up there's blood on her face and she is not interested in waiting until dawn anymore.
Jackson and his wife were moving to London so he could take up a post at the university. A teacher, like John Smith. And their house, the one he discovered the Cybermen at? Number 15, Latimer Street. I love this show. So if they got out that way, probably there's a way into the factory from there. So of course the Doctor tells Rosita to go back and be safe, and of course she tells him to suck it, and of course he sighs, but somewhere in there it's the most comforting thing he's heard all day.