"Oh my gosh Doctor. Your face!" cried Donna, leaping up from the floor.

"Uh, Donna, you might want to sit down, getting up isn't-"

"You idiot. You regenerated again didn't you? You stupid Martian!" cried Donna triumphantly.

"I'm, I'm not from Mars Donna" sighed the Doctor.

"Yeah, well you spacemen are all the same, whizzing off in your ships, sonicing things with-"

"Uh, hello?" said Clara nervously, "can someone please explain to me what just happened?"

The Doctor let out a long sigh.

"Uh, yeah," started the Doctor, "This is Donna." Donna gave a quick wave to Clara. "Donna and I used to travel together a few earth years back, when we confronted the Daleks."

"Daleks?" asked Clara.

"You'll find out sooner or later," remarked the Doctor, his hands twiddling nervously again, "Anyway, We were in big trouble, and the only way for us to get out alive and saye earth, was for Donna to absorb some 'regeneration energy'." The Doctor stopped, because Clara was giving him a very confused look. "I can change my appearance," he said, continuing despite the look of utter shock on Clara's face, "Anyway, this 'regeneration energy' holds a Timelord's essence, and by Donna absorbing it, she became part Donna, part Timelord."

"So why didn't she recognise you before" asked Clara curiously.

"Well, being a Timelord is a massive deal, there's so much knowledge and information, that the average human brain can't hold it, and in time will literally burn up. So to keep Donna safe, I had to remove that essence of Timelord, but that meant removing everything, all traces of me, the TARDIS, the Daleks and all of our wonderful adventures."

"Okay, but then how did she remember?" asked Clara, looking over at Donna curiously.

"Donna? What's wrong?" called the Doctor. For the past few minutes, Donna had been staring open mouthed at the TARDIS's interior.

"What have you done? It's less fungus-y. You've gone and changed the 'desktop settings!'" cried Donna.

"Yes, well I needed a change" muttered the Doctor quietly, "anyway how exactly did you remem-".

The Doctor was cut-off mid-sentence as the familiar, comforting grinding noise of the TARDIS had stopped. The temperature dropped what felt like a thousand degrees.

"Donna! What. Did. You. Do?" yelled the Doctor.

"Nothing! I was just re-calibrating the ship's time-rotor, and it kind of, well, stopped" said Donna, her voice whisper-quiet.

"Stopped? It just stopped?" asked the Doctor, glaring at Donna.

"Yeah, well, the TARDIS needed a bit of a re-tune! You always shoving it into fifth gear without letting it warm up!" replied Donna haughtily.

"Warm it up? It's a time-machine!" cried the Doctor scornfully.

"Exactly space-man, so if it's a time-machine, you can wait for it to warm up!" replied Donna, the usual sass creeping into her voice.

"Um, excuse me? But can someone please explain to me what's happening?" called Clara cautiously from the TARDIS's doorway.

"I re-calibrated the time-rotor and it-" started Donna.

"Effectively, Donna just stopped the engines mid-journey, leaving us stranded for a couple of hours, in a mystery location" snapped the Doctor.

"Well, isn't that exciting? I mean, there's a whole world out there to be explored!" cried Donna, leaping towards the TARDIS's doors. A cheeky grin crept onto the Doctor's face, the familiar spark in his eyes.

"Oh all right!" sighed the Doctor, "I guess I would've had to re-calibrate the rotor anyway".

"This is so exciting!" cried Clara, "Hold on, let me quickly grab something". She rushed off down one the TARDIS's many corridors, to her room. The Doctor then turned to Donna, a faint smile on his face.

"You know Donna, you never fail to surprise me" said the Doctor quietly.

"What are us women for?" laughed Donna.

"I mean, you're impossible!" cried the Doctor, "I wiped your mind, and yet here you stand with every single memory!"

"That's right space-man," replied Donna, grinning, "You don't know how much I've missed this". The Doctor looked at Donna confusedly, "I mean, I didn't know what I was missing then, but I felt, I don't know, sad," whispered Donna.

"Well, don't you worry Mrs. Noble," said the Doctor, "Finally we can finish what we started".

"Yeah, I'd like that" whispered Donna.

"Like what?" called Clara, from the other side of the TARDIS console.

"To finish what we started," said the Doctor, "with both of you". He threw the TARDIS's comforting blue doors open, and led the two ladies out, towards the big adventure that lay ahead of them.