A/N: Major spoilers for The Name of The Doctor. Don't read if you haven't seen it.
Inspired by this one line from the episode:
"...say it like you're going to come back."
Title is taken from Mumford and Sons' song "I Will Wait"
There were tears when she awoke.
They tracked down the side of her face at an angle, and she could almost still feel the brush of his thumbs against her cheeks where he had tilted her face up to his. She sat up in her too-bright bedroom; conference calls in the data core were not much different than they would have been in real life, so she had lain down to sleep on top of the covers in the middle of the afternoon when she'd received Vastra's summons.
There were two chairs and a small table by the window; the table contained two cups, steam still wafting up from them, and one of the chairs contained Charlotte, who waited with a calm that didn't match her young features. River's eyes met those of the girl for a long moment, then she closed them.
It felt like a dream, the realest dream she'd ever had, more real than any of the nightmares she had been so tormented by in her long life. How horribly bitter it was that his reality was now no more than dream fabric to her! But the tears were still drying on her face, and she could still taste his lips...
"He spoke to you."
It wasn't a question. River opened her eyes to look at Charlotte again, took a deep breath, and nodded. "He did, yes."
She planted her feet on the floor, standing a little unsteadily and moving to sit in the empty chair. Seeing no need to wait any longer, Charlotte took her own teacup into her hands and sipped at it delicately before speaking again.
"He's going to come back, isn't he?"
The words nearly knocked the breath out of her. It was no secret to Charlotte that the most secret dream River had held onto, the most buried hope she had, was that he would join her someday. She had always tried to tell herself that there was no reason to hope for that; how could she expect him to retire here? She doubted he would ever retire at all. So long in the Library she had waited for him to come, waited for him to contact her the way Vastra had, hoped and wished and prayed that even if he wouldn't join her, even if he couldn't, he would at least say goodbye. But now, after seeing him, after hearing Charlotte ask the questions...she knew he would do more than that. He would come back.
Overcome, River buried her face in her hands, pulling in a deep breath to steady herself...but her palms still held traces of his scent, and she sank from the chair into the floor with a muffled sob.
"River!" Charlotte was no longer the calm, wise-beyond-her-years computer mind; in an instant, she was on the floor beside River, small hands smoothing at the fabric of the older woman's shoulder somewhat frantically. "River, I'm sorry, I'm so sorry, please don't cry!" she pleaded, voice growing higher in pitch.
Drawing in a shaky breath, River moved her hands from her face to wrap them around the little girl, pressing kisses onto her brown hair. Charlotte pulled away enough to look up at River's face with the sort of apologetic expression only a wounded child can give. "I'm sorry, I shouldn't have asked-"
"He is," River interrupted, voice thick with tears. "He is, Charlotte, he is."
And suddenly she was laughing, and Charlotte was laughing, and the strange pair laughed themselves breathless in the floor of a bedroom in a house that existed only in memory. Because no matter how long it would take, she knew she could wait for him now.
River Song was exceptionally good at waiting for the Doctor. It ran in the family.