The Doctor was standing on the surface of his favourite planet, once again rescued from the jaws of destruction. He was surrounded by his friends, his family, all of whom had gathered together to save the Earth from its deadliest enemies. It was a marvellous, gorgeous, stupendous moment. Which was somewhat ruined by the TARDIS doors slamming shut and her dematerialising.

"Hey! Get back here this instant!" the Doctor demanded, he gave the TARDIS a few seconds to reappear and when she didn't he did a quick headcount. Rose, Jackie and Mickey were fingering their dimension hoppers, ready to make their own way home since their ride's gone AWOL. Jack was making bedroom eyes at Martha, and Sarah Jane was talking to her son on her mobile. The only ones missing are Donna and the other Doctor. They've nicked his TARDIS! Well, that's what being half human does to you, that lot will steal anything that isn't nailed down.

Somewhere in the vortex Donna slammed on the TARDIS handbrake. "Ha! So that's what stealing a TARDIS feels like."

"It was better the first time," said the Doctor.

Obviously half-inching the TARDIS while the original Doctor wasn't looking was not a decision they'd come to lightly.

"Let's take the TARDIS for a spin while they're all outside," the Doctor has said.

"Alright, Handy, but I get to drive," Donna had replied.

Back in the present Donna reached for the controls. "I can't wait to see the look on his face. I bet he looks like he's just been slapped with a kipper."

"Let's not go back just yet."

"Doctor..."

"Oh, please. He's going to leave me somewhere, he's going to kick me out of my own TARDIS and do a runner while my back is turned. I know because it's exactly what I would do. And if we go back now your brain will explode."

"What?!"

"Ha! Time Lord – Human metacrisis. Hadn't thought of that, had you? Not so clever now!"

"Oi!"

"Did you just pinch me?"

"Yes. Pay attention!"

"To what?"

"My exploding head, Dumbo!"

"Oh, but your head isn't going to explode. At least not as long as I'm here, cause we're the same, I came from you, so I can stabilise your neural pathways and make the metacrisis safe. And you're probably doing the same for me. I'm a Time Lord trapped in a human body; if I was on my own I might go crazy and start killing people."

"Oh, I definitely want to run off with you now."

"Oh, go on," the Doctor bounced on the balls of his feet. "It'll be fun and we can always drop the TARDIS back later." Donna still looked unconvinced. "We'll find a way to fix your brain."

"What are we waiting for, Spaceman?"

"Give it to me."

"You're going to poke my eye out."

"Don't tempt me."

Donna snatched the sonic screwdriver from the Doctor's hand. "I'm perfectly capable of scanning my own brain for signs of neural implosion." At that the Doctor burst out laughing. "What's the joke?"

"It's just that you, Donna Noble, temp extraordinaire, really are capable of it. More than capable of it."

"Yeah, yeah. Laugh it up, Time Boy."

"No need to be so tetchy, Time Girl."

"I'm the DoctorDonna, or DonnaDoctor, I haven't decided yet."

"And I'm the Doctor. Just the Doctor. There's no Donna in there, well, not much.

"Ah, I see you're –"

"No. Not married. Really, really not married."

"I was created from a brief and unwise contact with her genetic material. She's sort of like my mother. "

"Mother?" Donna objected to this in the strongest possible tone. Which, for Donna, was really quite strong.

"And I'm going to back away from that analogy slowly."

"We share a certain amount of DNA. You see, I'm a human being with the brain of a Time Lord and he's a Time Lord trapped in a human body. Which isn't nearly as kinky as it sounds."

"Hey," the Doctor shrugged in agreement, "I'm fine with any explanation which doesn't have one of us as the others mother."

The alien looked down her long hooked beak at them.

Later, once they'd been confined to their nice padded cell in the mental hospital Donna turned to the Doctor and said, "I think we might need to work on our introductions a bit."

"We're the DoctorDonna...Nah, can't say that, it sounds silly."

"Very silly," Donna agreed, and the two of them about turned back into the TARDIS and dematerialised.

The villagers who witnessed this little display ended up forming a religion around it. As organised religions went it was one of the better ones, devoted to being silly and getting distracted and wandering off in the middle of conversations.

"I'm the Doctor and this is Donna Noble."

"Very well, Doctor, Miss Noble, if you'll follow me."

"It's Doctor Noble actually." The Doctor raised an eyebrow. "What? I'm as clever as you, why shouldn't I call myself Doctor?"

"I don't quite think you're as clever as me, Donna."

"You're right, I'm cleverer."

"Doctors," their host addressed them, "if it's not too much trouble could we possibly focus on the massive alien invasion for just one moment."

I'm the Doctor and this is Donna, who's every bit as intelligent and impressive as me despite not having a Doctorate."

"Oh, please, Sunshine. As if yours is real."

Donna was sniffing him. He was trying to fly the TARDIS and Donna was sniffing him. "Is this some sort of weird human mating ritual?"

"You need to take your suit off."

"It is, isn't it?"

"You reek. You've been wearing that suit for weeks, and we spent all of yesterday crawling through those ventilation ducts. You're stinking out the TARDIS."

"The other one's got my brown suit, what else am I supposed to wear?"

"Well, I'd suggest clothes."

The inhabitants of the planet Travillian, like a lot of people before them, thought the Doctor and Donna were a couple. Part of the reason they thought this was that as they'd been dragged off to their separate cells for execution the Doctor had shouted, "No! She'll die without me!" Which sounded romantic, and also a little self centred and creepy.

By the time he escaped, found out where Donna was being kept and talked his way inside she was starting to experience the symptoms of neural implosion. She was stuck on the insults she'd been hurling at the guards as they'd locked the door, like a foul mouthed record.

The Doctor wasn't actually feeling too hot himself. He could hear his single heart thudding in his chest, and he was aware of his fragile human body aging.

"Get your filthy paws off me you-" Donna repeated once more before the Doctor touched her face and reached to her mind. "Oh, hello, Doctor."

"Hello. Shall we escape?"

"Not just yet. My head's banging." Donna rested her head on the Doctor's shoulder and the Doctor relaxed to the familiar sound of twin heartbeats.

The Doctor and Donna stood at opposite sides of the console avoiding eye contact with each other.

"Planet of the Psychotherapists, that was a bad idea," said Donna.

"Do you think we really do have a 'bizarrely co-dependent relationship?'"

"You mean apart from the bit where if we ever leave each other we'll both die horribly?"

"Yeah, really ought to see someone about that."

The year three billion and the human race are smack bang in the middle of their period of existing as Downloads. Very advanced medical technology for people without bodies, advanced enough to deal with a Time Lord – Human metacrisis. They were very keen on the Download thing, though.

The Doctor backed slowly away from the android nurse. "I was really just after something for this human heart of mine. A pacemaker maybe, or a pill, I like pills." The Doctor's back thudded against the wall. "No, thank you, I really don't fancy becoming a Download today, perhaps next week."

"You are not being given a choice," said the nurse. The air vents opened and the room started filling with gas.

"Ah," said the Doctor. "When my friend Donna comes out of neurosurgery could you possibly tell her where I've gone?" And resenting the human body for not coming with a respiratory bypass system the Doctor slumped into unconsciousness.

When he came to he was strapped to a table with electrodes attached to his skull ready to upload his mind into the planetary computer. He tried to speak but he was too groggy and then the machine that was going to inject him with enough tranquilizers to stop his single human heart was switched on. And then it was switched off.

Standing in the doorway was Donna wearing a hospital gown that didn't close at the back and talking about rewiring the planetary computer using only the sonic screwdriver and a lamp from her room.

"I take it the surgery went well then?"

"The DoctorDonna, now with a new and improved non-exploding brain."

"It's not that I'm not pleased for you but do you think you could untie me?" Donna aimed the sonic screwdriver at the Doctor's ankles. "Donna, do you know your hospital gown isn't closed at the back?"

"And I was about to untie you."

"And now? Donna? Donna? Donna, come back!"

The Doctor and Donna strolled out of the hospital with the apologies of the administrator for their inconvenience and a prescription for happy pills to stop the Doctor getting too maudlin about his human body.

"I suppose we'd better take the TARDIS back now?"

"I suppose so."

The Doctor, because he was still the Doctor even if he had no TARDIS or sonic screwdriver because his best mate and evil clone had done a bunk with them, stared out of Sylvia Noble's kitchen window. He was reduced to sleeping on Sylvia's couch on the grounds that Donna was bound to come back here eventually. Sylvia had started muttering about his getting a job and helping with the mortgage.

"Cup of tea, son?" said Wilf, placing a mug in front of the Doctor

"Thanks," the Doctor picked up the mug and promptly spilt scolding hot tea down his tie. "The TARDIS!" He ran into the back garden just in time to see the TARDIS materialise and squash Sylvia's begonias.

"Oh, hello, Doctor," Donna stepped out of the TARDIS followed by the other Doctor.

"'Oh, hello, Doctor?' You vanish in my TARDIS for whole entire days and all I get is 'Oh, hello, Doctor?'"

"Aren't you going to ask why my head hasn't exploded?"

"Oh, that."

"Yes," said Donna dangerously, "that."

"I took her to the year three billion," said the other Doctor happily, "they gave me some blue pills."

"To be honest it's been a bit knackering, I could really do with a long soak and a bottle of wine." Donna handed over the TARDIS keys, "If you could have the TARDIS back here in a fortnight." And with that Donna headed inside. The other Doctor gave a little shrug and followed her.

"This is my TARDIS it's not a time share in Spain!"

But they'd gone and the Doctor was left alone with Wilf who said, "We'll see you in two weeks then?"

"Yeah," the Doctor agreed. It could be worse, after all how long did your average human live?