Something was wrong. The Doctor had detected readings of a peculiar type of radiation. Time travel leaves its mark on a person, and the radiation was one of the tell tale signs. As far as the Doctor knew, He and Jack were the only 2 time travelers in the City.
He followed the trail through the City, not minding its occasional reconfigurations. He had been close, then the whole damn building moved. The hospital had taken the place of the structure that he wanted. Perhaps it was a start.
The Doctor flashed his psychic paper ID to the security guard at the desk, introducing himself as a Health and Safety officer. He walked through the hospital, paying attention to a small detector that changed pitch every so often.