The Doctor and Christina
London
“Little Blue Box, just as you said,” Christina said. The Doctor knew what she was going to ask next. “Right then. Off we go. Come on then, Doctor. Show me the stars.”
“No,” the Doctor said. He didn't want another person travelling with him, who he would get close to and then loose. Never again.
“What?” Christina asked.
“I said no,” he was beginning to imagine their travels. The constant questions about various things. The dangers, the near misses, and eventually him losing her to a Dalek that somehow survived the destruction of the Crucible, or some other foe.
“But I saved your life. And you saved mine.”
The Doctor knew where she was going with that reasoning. “So?”
“We're surrounded by police. I'll go to prison.”
“Yeah.” He was beginning to reconsider. Maybe just one trip. But unlike with Martha, he would put his foot down afterwards.