Ah, now there was a familiar voice. The Doctor paused mid-stride, foot hanging in the air, and awkwardly swung around using the leftover momentum. Familiar face, too. The 'young' fellow squinted for a moment, suspiciously, as if he thought Jack's sudden appearance might have been some sort of City trick.
Because he did think it might be a City trick.
Jack looked solid enough, though, and only conversation would reveal whether or not he was an impostor. The examining look evaporated, leaving in its wake a grin that was somewhere between pleased and self-satisfied. "Aha." The Doctor said, jabbing his finger in the former Time Agent's direction. "Jack Harkness." Why, the last time he'd seen Jack, they'd been --
Err. Well. That had been the last encounter from the Doctor's perspective, but in the City things seemed to be a little less predictable. As there was no way to tell where in his timeline this Jack was from, the Doctor decided not to say anything about Ten's last visit to see all of his companions.
He covered by leaning forward conspiratorially, even if his raised voice made any sort of private conference impossible. "I ought to have known you'd be in the thick of this, somehow. How long have you been in the City? Haven't seen a ginger girl, have you? Loud, Scottish, prone to trouble?"
The Doctor was absolutely confident that if anyone was to have spotted a pretty young (and immensely noticeable) young lady wandering about, it would be Jack.