Clara wandered into the control room and flopped onto one of the seats that ringed the exterior of the console.
"Headache again?" the Doctor asked sympathetically, noting the creases in her forehead, and the frown that marred her pretty features.
She nodded silently.
"Let me get you something," he offered. "It's not good for you to be in prolonged pain."
She nodded again, resting her head in her fist miserably.
"Back in a mo," he said gently.
"Is this normal?" Clara asked when he returned a few minutes later with something that looked a bit like an epi pen, but thankfully didn't sting or pinch or do anything other than start to relieve her pain a few seconds after he pressed it to the inside of her wrist.
"I honestly don't know, Clara," he told her seriously. "There's never been a human crazy enough to jump into a Time Lord's time stream before. I have nothing to use for reference. We sort of have to make this one up as we go."
"That's not very reassuring."
"I know, and I'm sorry. Can you tell me what brings these headaches on?"
"When I try to remember," she said promptly.
Sighing, he knelt before her on the deck and rested his hands on her knees. "Clara, I do know that the human brain is designed to hold the memories of one human lifetime, not the thousand or so lives that you've experienced. Forgetting is your mind's way of protecting itself."
"But I don't want to forget!" she wailed. "I don't want to end up like your friend Donna, who saved the universe and can't even recall your face!" She sniffled ungracefully and looked away from him.
The Doctor stared down at the deck for a long moment before trying to answer her. "Clara, wiping Donna's memories was one of the hardest things I've ever had to do, but it was the only way to save her life. Her mind was burning up…"
"I know," she replied in a small voice.
"And I don't think it will be necessary to do that in this case. I think if you just let your mind process through all the information in its own way, you'll be fine. It's when you begin trying to recall specific facts that these headaches start."
"But I don't want to forget it all! And don't try and tell me that it's OK, because you'll remember for me, because you won't! Most of the time, you didn't even realize that I was there!"
"I suspect that if you just stop trying to hang on to everything, you'll find that a surprising amount of information will be retained, just enough for your mind to handle. And I'm sorry - truly sorry - that I don't remember each and every one of you. You deserve better than that."
"It's not your fault," Clara murmured, trailing a hand down his cheek.
He smiled at her, then turned his face slightly to place a delicate kiss on the palm of her hand. "You know what?" he said brightly. "Even if you don't recall everything, and I don't recall everything, there is someone who does. Want to go see them?"
Clara nodded, and let the Doctor pull her to her feet. "You'll want to fetch a coat," he suggested.
Clara's eyes widened, and her face paled as she stepped out into the landscape of ice and snow.
"Clara, no!" the Doctor said sharply, realizing belatedly that a bit of warning might have been in order. "It's not - that place doesn't exist anymore - I'd never -"
She blinked, then shook herself, as if coming out of a trance. "Right. Of course…"
"This is a good place," he told her firmly, drawing her hand through his arm.
"Who lives here?" Clara asked curiously, looking at the twisting spires of a city that seemed to have grown rather than been built.
"A race called the Ood. There's one now, in fact."
"We welcome the Doctor and the Impossible Girl," the Ood intoned, with a slight bow.
"How do you know who I am?" Clara wondered. "The Doctor's the only one who calls me that."
"You saved the Doctor, and so by extension, you saved the Ood. We sing The Song of the Impossible Girl, so that the universe will always remember your courage and your generosity."
"Your people sing a song about me?"
"Would you care to join our circle and hear it?" the Ood asked politely.
"Yes. No." Clara bit her lip suddenly. "Actually…do your people sing a song about a woman called Donna Noble?"
"We do."
"Then…may I hear that one?"
The Ood turned its enigmatic eyes to the last Time Lord. "You choose your companions well, Doctor."