The swallow dipped and soared gracefully overhead, chattered twice, then wheeled and sped towards the horizon. Jessica watched it through misty vision until it had finally disappeared from sight, then groped a hand towards her pocket for her handkerchief.

"Allow me..."

She was neither surprised by the sudden appearance of the handkerchief offered to her, nor by the man who had appeared as if from nowhere beside her to offer it. She accepted it with a wavering smile. "Thank you."

"My pleasure."

They stood side by side in silence while she dabbed at her eyes and blew her nose. When she finished she offered the handkerchief back but he declined with a smile. "No thank you."

Jessica tucked it away in her pocket. "One year I will remember to bring one, I promise," she laughed. He laughed too.

"Oh, I don't mind. I have lots of them, and it's nice to be useful."

"Really." She turned and looked at him properly for the first time. She also wasn't much surprised to see that his face and appearance had changed again, but she knew it was him. His smile never altered, no matter which face he was wearing. That was unmistakably his. Those eyes, and the look they gave her, were unmistakably his as well. No one else ever looked at her like that.

"Yes." He held her gaze for a moment longer, then turned towards the horizon. "The last swallow of summer... always a sad spectacle."

"Yes."

"And every year, without fail, you're here to see him off."

"If I can."

"Yes." He looked at her again and smiled. "And every year, you ask me the same thing..."

Jessica smiled too. "Yes. And every year, you make the same reply..."

He cocked his head on one side. "Have I been wrong yet?"

"No." Her smile slipped a little. "But... I suppose there will come a day when... when the swallow won't return... won't there?"

She was almost afraid to look at him when she posed that question, but she did. His face was unusually grim, and for a moment, she was afraid he would say -

Then he smiled again.

"Not while I have any say in the matter. You can be sure of that."

"Promise?"

"Promise."

They stared at one another for a moment. Jessica had to reach for her - his - handkerchief and dab at her eyes again.

"Good," she finally managed to reply. "That's all I wanted to know."

***

The Doctor stood at the top of the hill and watched Jessica depart until she too had vanished from sight, like the swallow before her. She never looked back, not once, though he knew she probably wanted to. Sometimes he also thought she wanted to turn around and come back up to him.

Sometimes he thought he'd like to follow her down, to go back with her. The idea was so appealing sometimes that it made him itch, badly, and his two hearts, one in particular, would become heavy and slow, until it seemed as if only one was beating, and he'd suddenly feel as old as the centuries he'd lived through - only twice as lonely.

Then he looked up into the darkening sky - the empty darkening sky - and remember the promise he'd made. A promise he'd keep.

The Doctor started back down the other side of the hill toward the TARDIS and went on about keeping it; with both hearts beating as one.