None of the characters belong to me. I'm just playing in the BBC's sandbox for a little while. This is an one-shot fic.
"I'm still regenerating. I'm bursting with energy....
You see? The Pilot Fish could smell it. A million miles away.
So they eliminate the defence - that's you lot - and they carry me off.
They could run their batteries on me for a couple of years.."
-- The Doctor, "The Christmas Invasion".
***
Some things are fixed, some are in flux. The Doctor knew and felt that like no other. And at that moment, he stood in flux.
He took one look at the power core, and one at the small vial in his hand. As much as he was determined to do it, one memory made him sway.
"Time can be re-written!"
"Not those times, not one line, don't you dare!"
River. Professor River Song. That mysterious woman knew him in his tenth incarnation and probably beyond. Crash of the Byzantium, picnic at Asgard, those events she had mentioned with affection were to take place with him as he was now, he had been looking forward to them. But he hadn't lived them yet, he hadn't even seen River again after the Library. And now he was about to change everything, to do what she asked him not to, against what she died to preserve.
For the sake of 470 people on board that spaceship, and for his daughter Jenny, he had to. There was simply no other way.
The fluid universe waited for his choice. The burden of a Time Lord fell heavy on him once more.
I'm sorry, River... I'm so sorry. I hope that time will be kind after all.
He took the cap off the vial and drank the liquid inside with closed eyes. It tasted pleasantly sweet for a deadly poison. He had to smirk at that.
Within a second, the poison showed its teeth and filled the Doctor's body with excruciating pain. He gasped and grabbed the console. As soon as his cells realized they were dying, his will to survive kicked in. His inner energy burst out, hurrying to heal him, hurrying to give him new life.
Within two more seconds, most of the pain had gone. Now he had to do it. He directed his energy high up towards the power core.
The failing engines and batteries roared, all panel lights reversed from descending reds to ascending greens. In the bridge, the surprised captain ordered the helm's man to use the sudden peak of power and pull the ship out of its crashing course in full speed. Relief and cheers took the place of despair of imminent death.
Jenny couldn't think of how, but knew this was her father's work. She ran to the power core room to congratulate him... but her face fell at the sight. The Doctor's body was bursting with raw energy, and the ship seemed to drink it like a hungry infant nursing its mother. This was not good.
"Dad!!"
She used all the momentum of her sprint to knock him down and away from the console and then moved away from him. She watched in shock as the Doctor's body wobbled in uncertain form for several moments, a fluctuating mass of bright light, until it finally settled on the form of a different looking man in the same clothes.
"Dad!...", Jenny knelt at his side. "Dad, are you alright? What have you done?!... Dad?!!"
She kept shaking him. But the Doctor remained unconscious.
And time had been re-written.
Author's note: As you all probably know, David Tennant is stepping down as the Doctor in series 5, which means that River Song's story with him will be left untold, unexplained, or just ignored. I needed a good way to explain and accept that and I came up with this. I dedicate it to fellow Ten+River fans. If you enjoyed it, let me know, it'll make me smile. :)