End of the Road
Eventually, he returns her to France.
Everything that begins has to end. Life, time, even their one trip to the stars.
It's a trick that's kept her young and healthy. A trick of science and desire. Eventually time catches up to them. It always does. She starts to cough. His mouth tightens and his eyes go distant, and she knows that look. It's the look he had when they first met. It's the look of a lost man.
She puts her hand over his on the console, and some of the tension fades. He beams at her, but his eyes are still wrong, and she knows it's time to go. She lifts his hand to her lips. "If there is one thing I have learned with you, Doctor, and there are a great many things, it is that there is always just a little more time."
He stares at her for a moment before nodding. She enters coordinates into the TARDIS - how long ago was it that he taught her how to pilot his ship, their home? - and they begin to travel.
One last time.