Clohach startled awake at the sound of something clattering on the floor. The two male strangers were standing in the middle of the cell, looking frightened and guilty, a metal ventilation grill lying at their feet. Clohach's eyes tracked upwards to see the garish green hovercushion pressed up against the ceiling, right where the duct was. The back of the L-shaped cushion was towards him, blocking his view, but a leg covered in beige fabric and brown shoe dangled below it, so he knew the female was up there.

"Hurry, Donna! Save yourself!" the darker male shouted, and the leg vanished from view.

Clohach cursed and dove for the cell door, fumbling for the keycard on its chain around his neck. He wasn't sure he could leap high enough to catch the female before she escaped through the duct, but he had to try. Kshinle would have his hide for this.

As soon as he threw the door open, the paler male yelled, "Now, Donna!" And suddenly the cushion was swooping down towards him, knocking him off his feet, sending him crashing back against the far wall of the corridor. By the time he staggered back to his feet, the hovercushion with the female was halfway down the hall, the males running after it.

Donna whooped as she rode down the hall, kneeling on the seat and leaning over the back, feeling like Ben-Hur. The Doctor made a flying leap and landed on one knee on the left armrest. Donna glanced back to see Shaun struggling to get close enough to do the same, whilst the guard was now charging after them. "Come on, Shaun! You can do it!" She reached an encouraging hand back.

Shaun flung himself forward. He managed to grab onto the side of the chair back with his left hand, but his knees hit the very edge of the seat and slid off. Donna grabbed his right arm with both hands and clung on, as his feet dragged helplessly along the floor.

"Just let me go, love! Save yourself!" he cried.

"No way, you big oaf." She gritted her teeth with the effort. And then, just when it felt like her grip would fail, the Doctor tapped a button on the control panel, and the footrest rose up from the chair, catching Shaun's legs and allowing him to scramble forward to safety.

With the Doctor at the controls, they rocketed down hallways, around corners, up stairs, with dizzying speed. At last, a hard right turn nearly bucked them off, and then an abrupt halt pressed them all into the chair back.

In front of them was the storage room where they had left the TARDIS. But now the storage room door was wide open, the TARDIS rested on a wheeled pallet, and between them and their goal were four Ngskonites, plainly perplexed about how to fit a large box through a small doorframe.

The Doctor flashed his most charming smile. "Quite a puzzler you've got there. If you'll just stand aside, we'd be happy to take it off your hands." He pulled his key from his jacket, waved it at them.

The Ngskonites glanced at each other. They had no weapons, no comms to call for backup; they outnumbered the strangers, but just barely. Yet they had to try. In the narrow hallway, two abreast advanced slowly towards the hoverchair, whilst the others bided their time.

The Doctor's smile faltered. "Uh, would you believe that Kshinle said we were free to leave? No?" He watched the first two approach, saw their muscles coil. Just as they leaped, he shot the chair straight up, its occupants ducking to avoid braining themselves on the ceiling. And then just as fast, they were plummeting back down, pinning the second pair of Ngskonites to the ground. The Doctor jammed his key into the lock and threw the door open, and the travellers scrambled up and over the chair back, tumbling into the TARDIS. The Doctor kicked the door closed, and they all lay still for a moment catching their breath.

"Everyone okay?" the Time Lord asked at last.

"Yeah, I'm alright. Donna?"

"I'm fine. But what about those poor saps you just squashed?"

For answer, the Doctor jumped to his feet, stepping over her as she still lay sprawled on the grating, and turned the console monitor to face her. It showed their would-be captors shoving the chair from off of them, looking very indignant but no worse for the wear. An instant later, four sets of fists were pounding on the exterior, pulling at the door handle. But then the sounds faded away, replaced by the wheezing of an ancient time machine on the move.

Shaun propped himself up on one elbow. "We've probably just caused an intergalactic incident, yeah?"

"Oh yes. I imagine there will be an official protest. Earth might need to give them a discount on the price of CFCs, just to smooth things over."

Donna sat up. "The price of what now?"

Shaun laughed, scooted over to her, wrapped her in a tight hug. "Oh my girl, you've slept through so much!"

As the Time Rotor stilled, Donna was the first one to the doors. "Oh, I love this part so much!" She looked back over her shoulder. "Don't tell me, let me figure it out."

The Doctor gestured to the doors, and Donna flung them open and stepped outside, inhaling deeply. "Big city, obviously. Looks like Earth. Looks like twenty-first century. Looks like..." She stared up at the iron latticework soaring above her head. "Paris. This is Paris." She whirled, point an accusing finger at the Doctor. "You brought us back to Paris."

He frowned in confusion. "Well, I thought you'd like to get back to your holiday. But if you'd rather I take you straight home..."

"I thought we'd travel again. Like old times. Oh, I guess I should have discussed it with you, Shaun, but trust me, you'll love it, it's a brilliant life, so much out there to see and-"

"You can't," the Doctor said flatly, and she stopped, mouth still open. "I can leave you here, or I can leave you in London, but you can't travel with me."

She was frozen for a moment, then her face flushed. "So you had your fill of me, then? Finally got shot of me, and now you don't want me back? Or is it Shaun? Is that it, you don't want us with you because he's black? Of all the-"

The Doctor's snort was equal parts amusement and indignation. "If I've got no problem travelling the universe with an entirely different species, you really think I'd have a problem with some pigment variations within that species?"

"So it is me, then. I'm the problem."

He wrinkled his brow. "Why would I care any more about your pigment than about his? I travelled with another ginger once, actually. Melanie, her name was. She had a set of lungs on her. Not unlike you, come to think of it. I-"

"I'm not talking about my hair, dumbo! Is it...I don't know, you've raised the bar for your companions? I don't make the cut anymore? I don't meet your lofty Time Lord standards?"

His eyebrows rose. "No, Donna! It's not personal. You can't travel with me now, because you haven't travelled with me yet."

"What? What is that even supposed to mean? Have you forgotten all our time together? Did that machine wipe out your mem-"

"Donna," Shaun said in a quiet voice that still somehow managed to reach her. "Maybe just shut up for a minute and let him explain, yeah?"

The Doctor took a deep breath. "I thought you realized. The Doctor you met, the Doctor you travelled with - I'm not him yet. He's a future version of me. If you stayed with me here and now...well, tangling up the timelines like that is a fantastically bad idea, trust me."

"Oh." She was blessedly quiet for a moment.

"So what about you now?" Shaun asked. "Are you going to have to wipe your memory or something, so your future self doesn't know too much about Donna?"

"Nah, I don't think so. There are times when memory blocks are necessary, but in general, they're a bad idea - you never know when you're blocking some information that may be vital later on. In this case, I know we meet and travel and get our brains tangled, but I don't know when or how any of that happens, so I think it should be fine."

"But you told Wilf you couldn't fix her. Why would you say that if you knew about the ska-jean-back?"

"Ah," the Doctor grinned and held up a finger. "I think it's because I'll know about the skhaszhinbach. Can't imagine I would give up so easily otherwise. But I'll know that you have to meet and get married and come to Paris for your anniversary and run into me. That me won't be able to fix her because he knows this me already did."

Shaun shook his head. "This whole thing gives me a headache. But if you say it'll be fine, I'll believe you." He glanced between the Doctor and Donna, then reached out and shook the Time Lord's hand. "I'll leave you two to say goodbye. Thanks for everything, Doctor. I've never known the whole Donna - I'm looking forward to it. And I hope this isn't the last we see of you."

Then he was gone, and the Doctor and the companion he had never had were facing each other awkwardly. "How are you feeling?" he asked.

"Better. Much better, honestly." She hesitated, rubbed her hand idly along the railing. "Just...promise me. Promise me that once the timelines are straight or whatever, you'll come and find me. Me and Shaun."

"I promise," he said, lips stretched taut in a semblance of a smile.

She studied him a moment, then shook her head. "Pfft. No, you won't, I know it. I don't even know why I asked. You have the attention span of a gerbil. And I know I'm nothing special. I'm just a temp from Chiswick, but-"

"Hey now. No such thing as just a temp. Last alien invasion, there was this girl. Just a girl off a run-down council estate. Just a shop girl. And after I blew up her job, she wasn't even that. But it didn't stop her from being fantastic. Saved me, she did. Saved the world."

"Yeah?" Donna didn't sound convinced. "If she was so brilliant, why didn't you take her along with you?"

The Doctor shrugged, crossed his arms, looked away awkwardly. "I...I may have made an offer. But she had...responsibilities." The wrinkle of his nose revealed what he thought of that concept.

Donna was silent for a few beats, then said, "You're rubbish on your own, you know. You should go back, ask her again."

"Nah, I don't do that sort of thing." He didn't bother trying to refute her first statement. "I asked, she said no. No point in rehashing."

"Doctor, you've got to understand." Donna drew a deep breath, let out a long sigh. "Us humans, sometimes it just takes us a mo to wrap our heads around the concept of swanning off into time and space. I said no to you too. And then I regretted it, and it took me months to track you down. You wouldn't believe the garbage I had to wade through online. Don't put her through that, this...what was her name?"

"Rose. Rose Tyler."

Donna paused just a few seconds too long; when she did speak, she was making an obvious effort to keep her voice level and casual, and failing miserably. "Rose. Right. Well, if Rose really is so fantastic, she's probably kicking herself right now. Give her a second chance."

"I'll think about it." The Doctor was much better than Donna at concealing his frisson of excitement.

"Yeah, you do that, spaceman. By the way, did you tell her it's a time machine? I seem to recall you leaving that little detail out for a good long while with me."

He snorted, didn't reply, but tucked that idea away for future consideration.

"So," she pressed, "When I track you down again - and I will, believe me - you'll take me back? You're not just using this timeline business as an excuse because I'm some kind of annoying excess baggage?"

The Doctor leaned back against the console, stuffed his hands into his trouser pockets. "The thing about you, Donna, is that you care. You cared about me up on the Eiffel Tower. You cared about the crash victims; you cared when you thought we squashed those Ngskonites in our escape. Of course, you can also screech like a banshee. But presumably I get used to that at some point in the future. The caring is what's most important. It will be my honor to travel with you someday."

Her face flushed nearly as red as her hair, and before he could react, she had wrapped her arms around him, pinning his own awkwardly at his sides. She planted a sound kiss on his cheek, then released him and backed towards the door. "Take care of yourself, Doctor. I will find you. Just don't make it too hard for me."

"I don't doubt it, and I wouldn't dream of it."

And then she whirled out of the door, and he could hear her shrill cry, "Hey, Shaun, what about that dinner at Le Meurice you promised me?"

He smiled wistfully, paced around the console, feeling the sudden emptiness of the vast room. And then Donna's words floated back to him, "By the way, did you tell her it's a time machine?" He grinned at his reflection in the Time Rotor. "You know, I don't believe that I did." A twist of some knobs, a pull of a lever, and the TARDIS leapt once more through the Vortex.