Chapter 1: Cardiff, Wales, 1869
It was obvious Rose was upset, having nearly died only to stand and watch her planet burn while everyone else moved on. It was a familiar feeling to the Doctor and he realized, perhaps a bit too late, that he may have taken her to the end of the world for selfish reasons. Not to look impressive or dazzle her. Not to show off what his machine could do. He took her because he wanted someone else to know what it was like. To go through what he did on some small level. And she was the only one he had to show it to.
Feeling guilty, he took her back to her time to show her that things were okay, and he saw her watch the people go by with a morose look on her face. When he told her about his own planet she didn't offer forced condolences or palliatives. She understood. And when he told her he was alone in the universe she told him the only thing he needed to hear. He had her. He took her to the end of her world and she bared it like a trooper, smiled and took him out for chips. She certainly deserved something for that. A gift or a present.
Suddenly he smiled. He had no idea what he could possibly give this child in the usual sense, but he could give her something no one else could; time. More specifically a day. The one people most looked forward to each year. He could give her Christmas.
Back in the TARDIS he told her it was about time he took her to the past. Even let her help a bit by holding down the odd button or two. She screamed at him that it was never gonna work as he frantically tried to keep his ship under control but by the end they were both on the floor laughing.
"I did it!" He cried out happily, a bit of an I-told-you-so. "Give the man a metal! Earth, Naples, December 24th, 1860."
"That's so weird." She smiled, and he knew she'd picked up on the date. "It's Christmas."
"All yours." He swept his arm grandly towards the door, offering her all he could give her.
"But it's like. Think about it though. Christmas 1860. Happens once, just once, and then it's gone, it's finished. It'll never happen again. Except for you. You can go back and see days that are dead and gone a hundred thousand sunsets ago. No wonder you never stay still." She stared at him with wonder and admiration and he couldn't help hoping she'd always look at him like that.
"Not a bad life." He said it with some trepidation, because she never did answer when he asked if she wanted to stay or go home.
"Better with two."
And that's it. Deal sealed. She's going to stay even after everything she's gone though in the past few hours. Everything that he put her through.
He sent her off to the wardrobe to change and when she got back, he couldn't help it if he stared a bit. She'd seemed like such a kid, running from mannequins in baggy jeans and a hoodie, but there she was, all dressed up. He didn't have the heart to tell her that the dress she'd chosen was still a bit inappropriate for the time. It certainly looked good on her and she seemed so happy when he told her so. Who was he to break her illusion of being a period beauty?
He let her step out first to show her he really had gone there just for her. When he followed, he offered her his arm, an offer to guide him through this life of his. She hooked her arm though his and together they set out onto the pristine snow of a Christmas long past.