As she spoke, the Doctor's smile slowly faded. She had said it, all right - she wasn't his Rose. He had known that, of course, but he was realising that his Rose was never coming back. Still, if this Rose was from a different universe or whatever... oh, it was too much to think about.
"Mm, maybe," he agreed, not quite sure what he ought to be telling her. "It was nothing important. We just went undercover in a school once before. The teachers were aliens sort of pumping the kids full of this intelligence enhancing... oil... so that they could solve this sort of puzzle thing that would let them take over the universe. Same old story, y'know!" he said, a little bit of his smile returning although it didn't quite reach his eyes anymore.