At first, the Doctor is irritated when the TARDIS inexplicably decides to plunk him down in the middle of downtown Los Angeles in 2011. He'd had half a dozen other places he'd really rather have been, thank you very much. Not to mention he'd written off California in general as a bad job ever since that rubbish New Years in San Francisco a lifetime and a half ago (and oh, how much it hurts to think of himself as he was then, now). But then he happens upon the young dark-haired woman, cornered in an alley by the pilotfish roboforms she's somehow inexplicably attracted.
"Hello!" He calls cheerily from behind them, with a little wave. "I'm distracting you so she can hit you!" And she does.
When it's over, when the roboforms have been reduced to a deactivated heap between them, they look at each other, and know one another for what they are.
He looks human but is not. Neither is she.
He shows her the TARDIS and doesn't have to explain, because she understands how an entire world can exist within a seemingly tiny box.
She understands that everything is a miracle, that nothing is ordinary, that wonder is everywhere and anywhere for those with the capacity to look.
She understands the pain and the rage and the soul-crushing loneliness of last.
She refuses to travel without her own companion, a reckless young man whose world has suddenly been turned upside down—who's just realizing just how enormous the universe really is, and how dangerous, and how amazing—and even though the Doctor knows this Flynn bloke will probably drive him bonkers, he agrees to have him on board without a second thought.
The TARDIS may not always take the Doctor where he wants to go, but it always takes him where he needs to be, and for the first time since the end of the War, the Ninth Doctor is no longer alone.