The TARDIS had begun to groan, reminding Rose of a sick child complaining to her dad. The sound was familiar. Last time, the Doctor had been older and sadder, and his ears had been much larger. She had suppressed a giggle at the thought, recalling the first face that had been the Doctor to her. He might have looked a little odd back then, but now he was just plain crazy.

The Doctor was going on about wear on the engines and how she was a quirky old ship, explaining, "It's like a battery in your phone – after you've used it a lot, it doesn't work quite the same. Doesn't hold its power as well as it used to. Especially after the way we abused it going between dimensions into other London. Oh, you old girl, it's alright…" He trailed off, his voice getting softer as he began stroking the console soothingly.

Rose never interfered when he started petting his machine. She could see a swirl of emotions in his eyes when he did that, and she could feel all of his age at once in that complicated tangle. She wasn't sure she was ready to unwind that string and follow its length into his past. She wasn't sure he would welcome it.

So the girl kept quiet as he gazed into the central glass column. He was a child worrying over his new puppy when it sneezes for the first time, but also somehow an ancient man watching his old mutt fight off a familiar cold. After a few moments, she interrupted his thoughts, "Needs a top up, then?"

The Doctor nodded, eyes still on the TARDIS. "Yep. We need to put some more gas in the tank. Need a rift."

"Cardiff?"

"There are other rifts out there, Rose!" Bright eyes met hers at last "I could take you to the Medusa Cascade – oh, that's a sight! Or we could go to Darlington in 1965 and see the Dreadful Flap! That was an adventure. Maybe Arkheon, before it was destroyed! Beautiful planet, nice people, it's a shame the Daleks had to visit. There's a pretty safe one near the planet Kaesov, and the Owse are pretty cool, once you get past the tentacles…" He had started running around the console in his usual fashion, flicking switches and pulling levers and spinning dials with abandon, but she grabbed his hand to stop him "Doctor!"

He looked confused and maybe a little irritated, "What?"

"I'm sure those are all lovely places, but I can't remember the last time I ate. I think my stomach might be about to stage a revolt, and I bet they don't have fish and chips in the Medusa Cascade." She didn't mention that she might want to meet up with her mom for an hour or two as well, although this Doctor was much more comfortable with her "domestics" than the last regeneration. She needed to spend some time alone with her mother, to hug her, talk to her, and catch up how things were going for her. With Mickey in other London, fighting Cybermen like a real hero, Jackie was Rose's only tie to the normal life she was slowly losing. There were many things she was willing to give up to travel with the Doctor. Her mom was not one.

The Doctor looked a little disappointed, "But Cardiff is so – well – ordinary!"

Rose raised an eyebrow, "The last time we were in Cardiff, Blon tried to blow up the Earth and ride away on a sciency surfboard and ended up reverting back to an egg instead. The time before that, we were almost killed by the Gelth, only to be saved by Charles Dickens and a telepathic maid. Nothing is ever ordinary with you." The Doctor glared at her, his obvious exasperation clearly there only as an attempt to change her mind. Rose didn't budge – she was not in the habit of giving in.

Finally the Doctor caved. Heaving a great sigh and rolling his eyes, he changed the coordinates and began fiddling with dials and buttons again. She grinned and squeezed the hand she still held, "Thanks!" The bemused smile he threw her way reassured Rose that he wasn't as disappointed as he liked to pretend.

They parked alongside a familiar fountain, this time facing the opposite end of the square. The Doctor flicked a switch and spun a wheel and spouted some techno babble which Rose took to mean the TARDIS was now essentially a big solar panel. "Shouldn't take more than a few hours to charge up. Shall we?" He offered his elbow to her, and she looped her arm through it; "Absolutely!"

Setting off from the TARDIS, they began exploring Cardiff. Rose let the Doctor lead, even though she was perfectly familiar with the time period. He loved to play tour guide, and she loved to watch. After a dozen lefts and rights and a swirl of shop windows, Rose realized they were in a part of the town she had never seen. That was alright though – the Doctor knew where he was going, and it was more exciting to be somewhere new than to revisit. Besides, it wasn't like she would need to break off to meet up with her mother. After calling four times with no reply, Rose had decided she would wait until the next time she went home to do the catching up. Probably her mom was busy with a boyfriend anyway.

A likely looking shop appeared as she and the Doctor stepped around another corner, and they stopped to eat. Rose was halfway through her order of crispy golden fish and chips when she realized she was even hungrier than she'd thought and ordered a second helping. The Doctor, halfway through his plate and clearly almost full, eyed her voracity with something like incredulity, "Humans eat so much! Where do you put it all?"

"In our cavernously empty stomachs because we haven't eaten for two days! Relative time."

"Still, it amazes me. And possibly terrifies me a little."

Rose stopped eating and stared at the Doctor, a sudden question coming to mind, "Why don't you need to eat as much as humans? For that matter, why do you almost never sleep?"

He shrugged, "Simple biology. A Time Lord's body is better at processing the energy out of food and more efficient in using that energy. Same with sleep – we just don't need as much of it."

Rose watched him. There was something more; she could tell. She had come to know this face very well, and in most cases she could read it effortlessly. "Come on, there's got to be more to it than that!"

There was a long moment where the Doctor held her gaze unflinchingly before, "Well alright, that's only part of it." Rose grinned and did a mental fist pump as the Doctor leaned forward.

"The Time Lords evolved because of exposure to Time Energy, through a gap in reality we called the Untempered Schism. Part of that was our big brains and our ability to regenerate, but there was another part. Our bodies figured out how to convert the infinite energy of the Vortex into something they could use."

Rose felt her jaw drop, "You mean, you absorb energy? Like a plant?"

"Ehh, well, sort of like a plant?" the Doctor looked like he was struggling to create a better analogy, "But really not. If it helps you understand, go with it. Anyway, it means a Time Lord can go quite a ways before eating, especially if they are travelling in a TARDIS frequently. Not all of my biological needs can come from Time Energy – I need my vitamins just like any human, and occasional sleep does improve my mental functions –" he straightened up and glanced down at her plate again, "but it means I don't have to attack my fish and chips like a wild animal!" Rose laughed at that, but her mind was busy. She continued her meal, unusually quiet as she thought.

Finally she asked, "So how does regeneration work? What does it have to do with the Vortex?"

The Doctor stared at a point just above her head, his face scrunched as he contemplated how to present the information in a way she could understand. He looked at her, leaning forward and resting his elbows on the table. "Time Lord DNA shares many similarities with human DNA, but there is one big difference. At the center of it there runs a thread of the Time Vortex itself. A tiny slice of space time that a Time Lord carries with him forever. It's what allows me to see all of time at once – it is a part of me. When a regeneration starts, that thread superactivates, releasing a load of energy into the cells to repair them. All the DNA pairs get jumbled up, and have to find their way back together into a person. The sequence shifts, the cells repair, and you end up with a different face. But it's that little sliver of the vortex that really holds who you are. It's how Time Lords recognize each other, even in new regenerations."

Rose blinked. Then blinked again. "That's so –"

"What? Disgusting? Fascinating?"

"Alien."

The Doctor smiled, "Well, what would you expect from an alien?"

Rose laughed. Still her Doctor – everything was a wonder to be marveled at, but always he managed to give things context. He reminded her that even if it was new and strange to her, it was normal for someone else. She loved that.

They finished eating, chatting easily about their adventures and their next destinations. After another half hour of window shopping, the Doctor declared that the TARDIS was likely fueled, or at least would be by the time they found their way back. Rose followed his lead through the streets back to the fountain square. Somehow they had managed to get quite far away, and night had started to fall by the time Rose spied a familiar blue box parked alongside a tall fountain.

It looked more worn than she'd remembered. Hadn't it been a much brighter blue earlier in the day? Probably just the low light playing tricks with her eyes, she figured, but there was something…

The Doctor noticed something too, "Hang on, weren't we parked on the other side of the fountain?"

Rose furrowed her eyebrows, remembering, "I think you're right. Did someone move it?"

"Why would someone move the TARDIS to the other side of a fountain? I think if someone wanted to steal it, he would want to move it far away!" The Doctor ran up to the blue doors now, confusion written across his face. Suddenly his eyes went wide, and his hands flew into his hair the way they always did when he realized something important, "Oh, of course! Should have checked the time coordinates more carefully!" he turned to Rose in a blur of movement, grabbing her hand and pulling her away from the deceptively wooden doors, "We need to leave, now."

"But Doctor, the TARDIS is right here!" Rose tugged back, confused.

"No, that's the TARDIS from before. It's the TARDIS from when we stopped to refuel and captured Blon. It's the same day!"

At that moment, the timeworn blue door swung inward, and a familiar voice called back to someone deeper inside, "Just give me a mo. Need to check the surroundings before I take our resident convict to her last meal."

A ghost stepped out of the doorway, shutting his vehicle behind him. The Doctor had stopped trying to pull Rose away, resigned to the interaction. Rose stood like a statue of herself as she stared at the man now glancing around the square for signs of life. It was a moment before he noticed her.

"Rose? Did you forget something? I thought you and Ricky went off the find dinner and a hotel room."

A small part of her brain may have detected something like distaste in the undertones of that voice, but the rest of her was too much in shock to pay much attention. She took a tentative step closer, reaching out a hand to touch his forearm, squeezing it to convince herself he was real. She felt tears prick the corners of her eyes as she whispered "Doctor?"

Concern crept into his voice now, "Rose, what's wrong? Where's Ricky? And who's this guy?" He eyed the tall man with spiky hair and funny shoes standing behind Rose, "If he's done something to hurt you, I swear—"

Rose half laughed, half sobbed at the absurdity of that, "No, no, he's fine. He's a friend."

This did not seem to improve the Doctor's opinion of him, "And does he want to come along? Because I forbid it. My limit is one pretty boy per TARDIS, and Jack practically counts as two."

"Pretty boy?!" at last the new comer joined in on the discussion.

"Yeah, pretty boy! That means that no matter what she's told you, you are not coming- " the Doctor stopped mid-sentence as he turned his full attention onto the stranger who suddenly was so very familiar. He blinked, then looked down at Rose, and up again to the man standing behind her.

"Oh."

"Yeah… Sorry about this, didn't realize it was the same day or we'd have skipped ahead a few weeks."

The old Doctor nodded, then looked down at Rose again, but seemed unsure of what to say. Rose wasn't sure either, so she said the only thing that came to mind, "It's Mickey, you big dummy!" and she launched herself onto him in a massive hug, clinging to him like the last memory of a friend. She supposed in a way he was. This would likely be her last chance to see him as she's known him first. The war torn soldier who had needed her help to remind himself why the universe was beautiful. He had saved her in so many ways, and she had saved him too. And she knew what it was she needed to say.

Rose pulled away and looked him straight in the eye, "I know it hasn't happened for you yet, and I'll try not to give anything away, but you never gave me the chance to say goodbye. I know for you regeneration isn't dying, but so much changed that for me it felt like you had died. There was no way to mourn, either; the person that I knew just disappeared. I understand better now. But I still need to say this. Goodbye, Doctor. Thank you." She reached up on her tiptoes and kissed his forehead gently.

Then she turned to the new Doctor, taking his hand. Both Doctors stood silently. The old Doctor was confused; he broke the silence first, "Rose Tyler, there was never any reason to mourn."

The new Doctor squeezed her hand, and she smiled for them both, though she didn't quite understand. Then she broke the moment, "Right, Doctor, you have a dinner date to get to, and we have a universe to explore! Till the next time?"

She had meant it as a formality, but he smiled, "Always."

Rose and her Doctor turned away from the figure who was more memory than man. Rose let her mind tuck the memory away, and found that she thought of him not as a friend she had lost, but as a friend who had changed. Suddenly she understood. He hadn't died. He was still a part of the man who was holding her hand. Rose gazed up at the Doctor, seeing the echo of the man that was in the corners of his eyes. She grinned at him, "Hello again."

They strode towards the correct TARDIS, breaking into a run as it came into view. Running was second nature to her now. Sprinting headlong towards the TARDIS, hand in hand with the Doctor, towards the next adventure – there was no better place to be.