He was completely certain that with the destruction of Gallifrey, Ace had been one of the students to die, just another of the people he loved lost amid all the turmoil of War. He remembered wishing he had never sent her away. Wishing he'd never said goodbye.
Now! Now she was alive. And regenerated! Which was a positively terrifying aspect in and of itself. A full Time Lady. He doubted her rebellious younger self would've believed it.
He followed the instructions Ace gave him as carefully as possible---he landed in Cardiff first by accident, then somewhere else he had to run away from, and then, then he got it right. Shoreditch. Excellent name for a town.
He parked the TARDIS on a little streetcorner and stepped out. 2008. Just after the Year That Never Was. He even capitalized it for significance in his diary.
The question was, though! Where was Ace?