The two men had been dancing around each other—only half figuratively—for the better part of ten minutes, give or take. Susan wasn't particularly keeping track, and time was so hard to track some of the time, anyway.
It had begun with a creaking noise, followed by a small explosion, and then a rather larger explosion that contained a tall man in a fez and a bowtie, all perilously close to the good china. The man had come with a box, deep blue, which seemed to have been thefted from a police force somewhere*, out of which tumbled a tallish woman with the sort of irritated smile that marked her as a potential ally.
"Yes, yes, fine, you're a doctor, that's delightful, but Doctor Who?" Lobsang was significantly more frustrated about the sudden appearance of a box barely large enough to hold two people (and the requisite pair) than she would have credited.
The man in the fez threw up his arms, exasperated. "No, just The Doctor. And anyway. You haven't said who you are yet, though I do appreciate the whole not actively threatening things and I am rather sorry for dropping in on you like this. Very inconvenient of me. Very rude. I do mean it. But, see, this is definitely not the place I was trying to get to and I'd greatly appreciate it if you'd just let us get back into the box. And just. You know. Go." He flicked his hands, a shooing motion that was simultaneously eloquent and unhelpful. "Though, forgive the curiosity, but where are we? And who, precisely, are you?"
Something in Lobsang's expression shifted. Madmen who turned up out of thin air without permission were really very rude, and best to be startled. "Well. I suppose you could say that I'm Time."
The volley of "What?" and "What, what?" and "What do you mean Time?" and "What do you mean the Doctor?" and pointless arguing about archetypes and narratives went on for some minutes before Susan noticed that the irritated woman was outright laughing, now. Not loudly, just behind her hand. Their eyes met, and both women grinned.
And that was how Susan Sto Helit learned about interdimensional (accidental) travel over tea in her kitchen.
*Though clearly not Ankh-Morpork, as it was both reasonably clean and in repair.