Rose Tyler never did have a mind for science. Ten years old, she sat in the school library, pouring over her homework and trying to figure out what the book was saying. Her teacher, impatient and overwhelmed by the sheer number of students he taught, wasn't much help, so Rose had long since figured she was on her own. So when a shadow fell over her papers that day in the library, she was certainly not expecting what happened next. A man stood behind her, peering at the list of review questions with which she was so struggling. As an adult, Rose could never remember if this man was old or young- the distorted view of age in childhood made judging accurately almost impossible- or if his eyes were blue or brown, or if he had dirty blond or brown hair. But he smiled at her, and asked her if she could use some help with her homework. Young Rose eyed him carefully.

"Who're you?" she asked, pretty confident she'd never seen him before.

"I'm Dr. Williams. Science tutor. Just helping out here for a while 'fore I have to go back to the States," he introduced himself. "Hoped I might be able to help you out, Miss Tyler?"

Rose wasn't about to turn down help on this muddle of science-y stuff in front of her. "All right. Why not?" Dr. Williams sat down next to her. Looking over the papers in front of them, he reached in his pocket, fumbling for a pencil. Rose held out hers. "Here, use mine." With a smile, Dr. Williams took the pencil and pulled over one of the homework sheets.

"Let's get started."

Over the next six weeks, no one could believe the sudden uptick in science grades across the school. Dr. Williams' tutoring was apparently having a wonderful effect on the young students. His medical knowledge, combined with an obvious love of science, made him an ideal tutor, while his occasional wild stories of the things he claimed to have seen made him incredibly popular among his young students. And first among his admirers was one Rose Tyler, who utterly adored the man who was the first person to make her not feel dumb. For the first time, she actually looked forward to school because she no longer struggled to keep up. If he was honest, Dr. Williams had to admit that Rose was his favorite as well. He genuinely enjoyed helping her with her homework, relishing every time the light went on in her eyes that meant she understood something new. She was engaging, funny, and so much smarter than she thought she was. Just like he'd expected.

But the day did come when Dr. Williams had to leave the school. After all, he was only a temporary tutor while they found a full-time teacher for the job. Although he'd known he couldn't stay, there was no way for him to stay, he couldn't help feeling rather sad at the idea of leaving these children behind. It made him so happy- and also was a bittersweet reminder of what he had missed. On his last day, Rose was the last student he worked with. Near the end of their session, she looked up at him sadly.

"'S true, isn't it? You're leavin'?" she asked. He nodded. "But why? Where are you going?"

He looked down at the trusting little golden girl next to him. "I have to go back where I came from. I'm sorry, Rose, I am, but it's the only way."

"Will I ever see you again?"

"Maybe. I'd like that, wouldn't you?" Rose nodded her assent. As they got up to leave, she turned towards the man who had helped her so much. Impulsively, she threw her arms around him.

"I'll miss you. And thank you. For everything." Surprised but glad, Dr. Williams wrapped his arms around the small figure latched onto him.

"And I you." As they hugged, he felt a slight pressure against his chest. Pulling back and reaching into his jacket pocket, he discovered the pencil Rose had lent him on the first day they'd met. He held it out to her. "Here. This is yours, isn't it?"

Rose shook her head. "No, you keep it. Wait," she reached into her pencil bag, fumbling around for a minute before extracting a small eraser in the shape of a pink rose that fit over the pencil's nub of an eraser. Grabbing the pencil, she put the new eraser on top, then handed it back to him. "There." They paused for a minute, before Rose quickly slung her bag over her shoulder, not wanting to let her tutor see her eyes watering. "Well, goodbye then."

"Goodbye." Dr. Williams began to walk out, then stopped and turned back towards the blonde girl. "Rose? Don't forget- you're smart, much smarter than you think. Trust me. Just- be amazing, okay? Be brilliant. Be fantastic." She grinned.

"I will."

And she did. Over the years, Rose forgot a lot of the science Dr. Williams had taught her. Okay, almost all of it. The sound of his voice faded from her ears. Eventually, she could only construct a vague idea of his face. But what she never forgot was that final request he'd made of her. She tried her best to live up to what he'd taught her and what he'd asked of her. She tried her best to be, as he'd said, "fantastic." And one day, years later, when a stranger with big ears and a leather jacket used that word, she trusted him more than ever.

The tutor collapsed into his chair at home, spent by the day's events. And now he was home again. In another room, he could hear Clara settling back in, but he'd already decided not to tell her where he'd gone for the past few weeks. He'd used the name of one of his best friends, just because of how much he missed them, the girl who waited and the last centurion. He remembered back to the day he'd almost died, and all the things he'd wanted to do. At least he'd gotten to cross one of them off that list he tried to ignore, he thought. Looking up at the shelf nearest him, he passed his hand over a handful of pictures. There was one of his family- quite literally: his arms wrapped around a curly-haired blonde on one side and a redhead on the other, whose own hand was taken by the blond man next to her. But there was an earlier picture he found too, one that he couldn't help smiling as he looked at, though the smile was half glad, half bitter. Another family of his, a little earlier than the first, in which three people grinned. Himself, in his big-eared, leather-wearing body, an impossibly handsome man with a confident grin, and between them, a lovely blonde woman. He traced the picture, just slightly, unable to ever let go of one of the greatest loves of his very long life.

I could help Rose Tyler with her homework.

And he did.