The Doctor paced around the room with his hands clasped behind his back, staring at the TARDIS coral.
How? How did it do this? It had to have locked on to something. Some sort of power or energy source to be able to manipulate this one little room into being able to go through the time vortex. But that would require an enormous amount of energy and they were in a forest in 1974. What could have possibly produced it here? And how, on Earth, would they be able to get back?
He started sonicing the tank again and scribbling down readings in Gallifreyan and English. The coral still seemed to be honed in to some sort of power source but whatever it was, it was very good at cloaking itself. If he could just figure out what it was, then he could probably harness that energy and use it to take them back to their own time.
After slamming his hand into the side of the tank in frustration, he hissed, "Oh, c'mon! I don't want to be stuck here. Your batteries are going to go dead soon and I don't have the technology here to repair you!"
He had hidden that latter part from Rose. He didn't want her to worry. But now, he was beginning to think that getting stuck in 1974 was a definite possibility. He could feel panic and aggravation rising up inside him like a hot wind.
Then, the lights started flickering.
On and off; off and on they went. There was some sort of screeching reverberating around him. The Doctor spun in circles, trying to find the source of the dreadful noise, but there was nothing in there. It was coming from all around him. He was having trouble keeping his balance.
Suddenly, the TARDIS coral started to give off this putrid, yellow glow that pulsed with the noise and lights. The Doctor fell to his knees in front of it and tried to aim his sonic screwdriver at it to find out what was going on. However, the moment that he touched the side of the tank, he felt a shock and was thrown backwards across the floor.
And everything went black. Everything that is, but his hand that had touched the tank. It was glowing with a fiery, otherworldly light.
"Regeneration energy," he softly gasped as he stared at his hand, mesmerized. "No, that's not possible."
The light was gone as quickly as it had come and he was left in complete darkness. There wasn't even any noise. All he could hear was the sound of his own breathing and the beat of his hearts.
Wait! He thought. Hearts? No, no! I've only got one now!
But he could feel them. He could definitely feel two hearts beating in his chest. And they were beating wildly out of control. In that moment, he knew he was going to pass out…
When he came to, he was sitting next to the TARDIS tank with wires in his hand. It only took a moment for him to realize that he had ripped them out of the tank and he was now staring at the broken environment that he had created. All those hours and days and nights of work…gone. It was gone. He had killed it.
The Doctor dropped the wires and pushed himself along the floor away from the tank. He had trapped them there. They were stuck now. There was nothing that he could do.
Why did I do that? He thought. How could I have done that?
Then, he remembered the lights, the screeching, his hand glowing, two hearts beating… He felt his chest. Only one heart; there was only one heart.
His thoughts swam from regeneration to the Valeyard to so many other dark places.
"I'm going mad," he whispered to the empty room.
