He turned up on her doorstep with a new haircut and a suit.
River's face registered surprise for a moment, then her lips curved into a smile. "Hello, sweetie," she said.
The Doctor's hearts ached at how familiar that phrase had become. He forced out a hello and stepped into her house.
It really was beautiful. Her walls were lined with shelves of books, a life's worth of research. There was an underlying theme only he would have caught: on one shelf he briefly saw a collection of Charles Dickens' works, Agatha Christie novels, William Shakespeare and Pompeii's history among others. He spotted lipstick that looked suspiciously like her hallucinogenic tube on a table, and a carved wooden desk for her work at the University. Papers with the Luna University's crest sat messily piled in a corner, her loopy writing filling them.
Time snapped back into placed as he followed River in, storing all he'd seen into his long-term memory. "You're all dressed up," River said with a smile. "I assume we're going somewhere?"
"Actually, yes. The Singing Towers of Darillium," the Doctor said, trying not to betray what he was really thinking.
"It's parked outside, right? You haven't lost your TARDIS?" River asked with a stern expression. "You know, you could time-lock it and no one could get to it."
"Yes, but there's a small probability that the system malfunctions and the TARDIS becomes a fixed point in time – who knows who could be drying their hair around there –" the rest of his words were lost as she yanked him out the door.
He tried to get one last look at the warm, golden interior of her house, but was whisked away to the TARDIS. This was all going so fast. But that was what was so enticing about River at the same time – she could make a moment last forever, every detail of her etched into his mind, the shape of her lips, the exact shade of her eyes, that stray curl she brushes back from her face constantly; she could make two words drip with meaning, and all that in one "Hello sweetie." But then the next moment, when she was truly comfortable, she'd sweep him away in that whirlwind way of hers, when her every motion held promise of her beautiful laughter, so trusting of him, her Doctor, as she loved to insist.
And at that moment he knew her trust in him wasn't well placed. What would her life have been without his involvement? Melody Pond, happily living with her parents, never having been brainwashed. Melody Pond, able to spend the rest of her life as she wishes, not living a half-life full of programmed children.
But it was too late now as he sped into the TARDIS. She took control of the console as had become a habit between them. Every once in a while she smirked, and in that small motion she teased him about flying the TARDIS half as well as her. He sat back this time, watching her hand seamlessly grab for the hammer, as she pushed levers, checked the time rotors, and peered into the machinery to verify everything was functioning.
He'd never asked how she'd figured out TARDIS secrets he didn't know himself. There were so many things he didn't ask.
She smiled at him as the TARDIS stilled. "Smooth landing, Captain," he said.
"Am I a Captain now? I've been a Professor, Admiral, and a Co-Pilot, but never a Captain. Captain Song. I'll add that to my to-do list."
The Doctor tried to smile and not think of how painfully short her to-do list really was. "Come along, Pond," he said, taking her arm.
They stepped out and River let out an audible gasp. "Is this really…?"
"The Singing Towers of Darillium," the Doctor finished quietly.
River looked at him, her eyes shining. "I can't believe… Oh, it's so beautiful," she said, her voice sounding fragile. He looked over at the horizon, trying to find an excuse to tears his eyes away from her beautiful face, and all his guilt.
It really was beautiful. The sky was pitch-black, dotted with the occasional turquoise pinpoints he knew to be what was left of a centuries-old nebula, suspended in the artificial atmosphere of Darillium. The two towers jutted out, made of sandstone, "authentic and imported from 60th century Earth," the tourist guides announced proudly. They were brightly illuminated, their organic, rough shape smoothed into place by a stream that flowed from the tip of each. It fell slowly down the towers, creating rivulets and looking like a shining sleeve perfectly molded to the towers, making them look completely reflective, flickering slightly under the bright lights trained on them. They leaned towards each other, like massive creatures reaching for one another infinitely slowly, fingers reaching out blindly in the dark.
"Beautiful," he agreed. "Five… four …" he murmured, squeezing her hand. She waited breathlessly in anticipation.
Then the entire sky exploded.
River shielded her face with as iridescent sparks slowly descended to the ground, like bizarre snow. When her eyes got used to the sudden brightness, she saw that the towers themselves were glowing, and the air was charged with electricity, almost to the point of humming.
As the humming got louder, she realized it was a melody. It was simple, really, four notes in a sequence, but to her it seemed like the most elaborate, delicate thing imaginable.
The Doctor didn't wait for her to ask, and he plunged into the explanation. "The water passing over the ridges creates notes, and together they make a song. During the day, the four suns cause most of the water to evaporate. The Towers only sing at night."
River smiled at him. "This is perfect."
He pulled something out from his pocket, and in the semi-darkness, placed his sonic screwdriver in her hand and curled her fingers around it.
"Don't lose it," he said seriously.
"What, like I would," she said jokingly, then caught sight of his face. "Why are you giving me this?"
He looked resolutely out into the horizon, looking out at the Towers. River took his face in her hands and gently turned his head to face her. He looked at her face one last time, knowing they'd have to leave soon, and a single tear slid down from his left eye.
"Sweetie, you can tell me," she said. For a moment he considered ripping all of space and time apart and telling her, and pointlessly trying to escape a fixed fate.
"Spoilers," he said, trying for a smile.
And a few days later the TARDIS notified him that the Library had reopened, and it really felt as though he'd never smile again.