The Doctor knew he couldn't go back for Reinette. After entering her time stream after her death, there was no way he could go back in time and find her, even with the TARDIS…
But he hadn't really entered her time stream again, had he? He had entered the king's, yes, and he had let the time pass in her life, but that wasn't the same as having met her again. He thought of her warm mouth on his, her quick intellect, the way she had reached into his mind as no one else had, and seen and understood the darkness there… She was a magnificent woman, like none he had met before.
He decided he didn't care. He gritted his teeth, smiled a little, pressed a few buttons on the console and jammed the lever down, ignoring the voices in his head that were telling him how reckless he was. The TARDIS wheezed and landed heavily, and when the Doctor realized how quickly he was breathing, he slowed it down; he heard Rose calling from behind him, but he walked slowly to the door. He leaned his forehead against it, turned the handle, took a deep breath. He opened the door and popped his head out.
"Fireplace man!"
He grinned and hopped out of the TARDIS, and saw the face he thought he would never see again.
"Reinette! Is your bag packed?"