The globe on the top of the TARDIS blinked sleepily, the blue box pitched precariously on the side of a rocky crater. The Doctor had made many stops to this moon over the years, though on outward observation, there was absolutely nothing spectacular about it. It was uninhabited, physically unexceptional, and visually uninteresting. A keen or well-travelled eye, however, might notice that it was odd in a single way – it was a moon, yes, but it seemed to orbit not around a planet or system, but a vast and empty patch of sky.
The Doctor was perched on a boulder a short distance away, head held up with his hands. His eyes were somewhat glazed as he stared off into the empty, spiraling space, his mind seeming to wander through memory.
Suddenly and apparently unprovoked, he jumped off the boulder and seized a rock off the dusty moon surface, flinging it as far as he could with an angry bellow. The roar echoed off the rock ominously.
"Now, what is that going to achieve?" came a disapproving voice from behind him.
"River!" growled the Doctor, recognizing the voice immediately and pivoting around, face twisted into an uncharacteristic scowl. "What are you doing here?"
"Looking after you. You never seem to be able to do it yourself." River answered matter-of-factly.
"You shouldn't be here." the Doctor snapped, turning back towards the patch of empty space and sitting down on the dusty ground.
"Neither should you." River replied, sitting down beside him. "Or I assume you shouldn't, seeing as the effort you went through to be alone. Jumping around here and there, switching times like they're going out of fashion – one might think you didn't want my company!"
She cast a look around the desolate, barren moon, before adding: "I'll admit, I was expecting something more dangerous."
"You don't know why I'm here?" the Doctor asked incredulously.
"I haven't the slightest clue why you're here." River replied honestly. "I mean, if you wanted a nice moon to rest on, you really should have dropped by Jupiter."
The Doctor laughed, but the sound was entirely void of humor. River gave him an anxious look. The Doctor, catching her concerned glance out of the corner of his eye, smiled brightly and entirely falsely.
"Where are we, anyway?" River questioned, frowning as she looked around.
The Doctor looked up at the empty sky, eyes seeming to shine somewhat more than usual.
"This is where Gallifrey used to be." he answered, with considerable difficulty.
River's face dawned in sudden comprehension. "Oh, Doctor, no, you shouldn't have come here-"
"I always come here. On this day, every year." the Doctor stated.
"And always alone?" River asked weakly.
"Always. Well, until now." he amended.
But why? Why here, why today?" River asked, frowning,
"Because," the Doctor began, drawing a deep breath. "This is the day that I killed them all."
River's jaw quivered very slightly, and her eyebrows turned up in distress for just a second, before she regained a poker face. She hesitated for a moment, before frowning deeply.
"Why on earth would you do that to yourself every year?" she said angrily, swiping out and smacking his arm scoldingly. "Why would you come here, just to-"
"You know why, River." he snapped impatiently, turning to face her with eyes that were equally pained, desolate and furious. "I come here to remember them, every last innocent soul that I murdered in cold blood."
His voice cracked, and he paused for a second to regain his composure before finishing.
"They were my own people, River, and I destroyed them. Every last one."
"You had no choice-"
"I DID HAVE A CHOICE!" the Doctor roared furiously. "I had a simple, two-way choice, and I chose to do exactly was the Daleks had been trying to do for centuries – exterminate the entire planet!"
"But you destroyed the Daleks, too, and saved countless other systems from the same fate!" River cried. "You acted for the greater good."
"Well, sometimes the greater good just isn't enough." the Doctor snapped.
River sighed, and put her arms gently around his shoulders, cradling him whilst he trembled slightly.
"What is it that you said to me when I had to do the one thing I dreaded more than all else?" she said quietly. "When I had to kill you – you! - on the beach, at Lake Silencio."
"I told you that you are forgiven – always and completely forgiven." the Doctor murmured distantly.
"Exactly. And I know that you are, too." River replied, stroking the side of his face in a gesture that seemed as natural as breathing.
Neither of them took any note of how long they sat there, the Doctor cocooned in River's arms like a child. Finally, River spoke.
"How many times must I tell you, Doctor? Don't be alone, not even on days like these. Especially not on days like these."
The Doctor nodded and forced a smile, and thought that, so long as he had River, the darkest days might not need to seem quite so dark.