The Doctor stared down at his new hands, mind warm, buzzing blank with the regeneration energy. He was younger, he knew that, but something that wasn't the golden energy was burning in his gut, and in the second before he remembered what it was, a tiny voice cried out that he didn't want to know.
But he did know. The reality that he had killed all of his people descended on him like a thousand Dalek battleships.
And it crushed him.
The Doctor didn't know how long he floated in the red haze of agonizing regret, but he knew when it stopped. He knew what pulled him out. He knew the only thing keeping him from falling into a coma of hurt was the elusive, shadowy memory of golden hair and a smile, and the barely remembered whisper of bad wolf.
He couldn't explain that. He couldn't explain where that face and those eyes full of light came from.
The Doctor couldn't explain it, and what does the Doctor do when he can't explain something? He finds an answer no matter how lost he is. He keeps searching.
After years of searching the corners of the universe (or was it trying to escape his last regeneration?) he found himself in London again, still running.
It was London, so of course some aliens had a nefarious scheme up and running, with shop dummies coming alive.
He should have known that as soon as he stopped searching he would find her. When he saw that face searching for someone called Wilson, he realized he didn't know why he needed to find her, or even if the memory of her face had been something more than simply a dream. He didn't know what to do next, but then he rarely did.
So he took just her hand and whispered…
Run!