"Sally Phelan didn't die for nothing," says the Doctor. "Because that's the key. The emotional inhibitor -- if we could find the code behind it, the cancellation code, then feed it throughout the system into every Cyberman's head..." Mrs. Moore nods. "They'd realize what they are." And then what? "I think it would kill them." The Doctor's brow furrows, but I think he's just asking for the audience's sake, because the answer is obvious: "Could we do that?" Mrs. Moore instructs him that they have to, basically, because the next step is that more and more people die. The Doctor makes a sad thinky face. I don't know what the problem here is. "There's no choice, Doctor," says Mrs. Moore. "It's got to be done." Um, first of all, they are already dead. The soul's not located in the brain. Secondly: what, you only like the kind of enlightenment that feels good? You only want to wake up if breakfast is ready? You'd rather stay asleep if it's a Monday? That's never been how the Doctor works. He wakes you up without regard to your personal happiness or what stupidity you'd prefer. It leaves marks and scars and holes in the world, but there it is: everything ends. Even ignorance. A Cyberman is standing right behind Mrs. Moore. And then her neck is snapped, and she is dead. The Doctor shifts from pain to sadness to horror, and then on into rage, fury: "No! No! You didn't have to kill her!" The Cyberman offers to take the Doctor for analysis, because it doesn't recognize his two hearts, and the Doctor, sickened by the death of Mrs. Moore, allows himself to be taken.