The old man trudges across the desert, bag slung over his shoulder like Father Christmas. But no teddy bears or wooden trains rattled in the sack, no ribbons and wrapping paper poked from the top. "No more," he murmurs to himself. "No more."

He should just do it. Do it now, and get it over with. Every moment he delays-What does it matter? They will all burn anyway.

A worn, wooden hut sits on the horizon. No grand history, no mighty spires–just a shed. One more layer to hide himself from any watching eyes. Like a child closing his eyes during hide-and-seek, it won't make a difference to anyone but him.

Still. It will do.

The floor is littered with bark and leaves; light filters through the roof. He sets the bag down, unfolding the wrapping to reveal it: the Moment.

It doesn't look like something from the Omega Arsenal. It doesn't even look like a weapon at all, really. Just a wooden box, engraved with concentric circles, set with winding metal gears. He nudges one, then another. "How do you work?" A raised labyrinth, sliced into hundreds of dead ends. "Why is there never a big red button?"

Is someone there? Despite himself, the man strides to the door and lifts the latch.

Nothing. Of course nothing.

"Hello? Somebody there?"

"Doctor," someone speaks behind him. A woman's voice, British accent. Something yellow moves, just out of sight.

Bright yellow, like dandelions and butter and the sunlight on Earth. Orange boots–no, willies, how could he have forgotten the word?–kick at the mulch, while her elbows rest on her knee. "Don't sit on that!" he orders, grabbing her by the arm. "It's….Sarah?"

She breaks loose, rubbing her arms. "Is that any way to great an old friend?"

"I'm sorry, it's just that…it's been a long, long time." He chose to be alone this time. He had good reasons. But even so…

"That's more like it. But as it happens, I'm not."

"Not her? Then what are you?" Clone? Android? Hologram?

"They must have told you the Moment had a conscience."

He stares at her. The same yellow mackintosh, the same wavy hair, the same bright eyes. Of course it can't really be Sarah, not his Sarah.

"I can see everything: times that were, times that never were. You've been here before, both of you."

"No. She never came to Gallifrey."

"Not here," she pointed to the Moment. "Here. Except it was smaller, and simpler: two wires. If you had the choice now, what would you chose?"

"It's pointless. That point's deadlocked, can't be changed."

"It's the same question. 'Do you have the right?' All those lives lost since that day, all those dying now. Has it changed your mind?"

"If you've seen my past, my present, then you know what's happening now. Why I took you from the vault. Every moment in time and space is burning. It must end. And I intend to end it, however I can."

"And you'd use me to end it. Is that your mission? All those errands, all those times they made you do their dirty work, were they preparing you for this? The weapon they wouldn't dare use, speaking with the voice of an old friend?" Her voice rose. "What if I was her? What if she knew? I could show her everything, the raw recruits trapped in an endless cycle of regeneration, the Could-Have-Been King…the children."

"Stop it. You're not her, she wouldn't say that, she'd never say that!"

"The children. You were so young then, when she was with you. Barely more than a child yourself. And now?"

"This is where it ends. I've accepted it."

"No," the Moment steps aside. "That's not right."

"What?" He can only see her silhouette. "What do you mean?"

She picks up the box, admiring the runes on one side. But she's older, at least forty, dressed in a white blouse, brown vest, trousers, sensible shoes. "Just a little change. You meet again, did you know that?"

"Sarah?"

"She'll be old, the next time you meet. Older than you, by some people's standards."

"Do I tell her?"

"Spoilers," she wrinkles her brow. "That wasn't her line. Another person, another place. But suppose you did. What would you say?"

"I'd say…I'd say," he sits down. "Oh, I don't know. Why are you asking me?"

"Because you'll ask yourself. When your sleep is haunted by nightmares, when you're singled out time and time again as the last of your kind, when you wonder just how human you can be–you'll ask."

"The future? I won't even have one. Not unless–" he glances at the Moment again. "I don't have a choice."

"There's always a choice."

Inspired by an entry on TV Tropes headscratcher page for Day of the Doctor:
If the Moment chose someone like a family member, old friend, former teacher, maybe even an old enemy etc, having someone like that ask "Are you sure you are ready to kill billions of innocent people" instead of a complete stranger (from their perspective) makes you question it more.
Also, I'm not sure if there will be more or not.