Heading into heavy spoiler territory, with plot from the Stolen Earth making an appearance here. You have been warned.
The trio return to the Tardis, the Doctor explaining to Rose about his meeting with the Daleks in 1930's Manhatten and how Dalek Caan is the last surviving Dalek of the Time War, just as the Doctor is of the Time Lords. The Doctor ignoreed Jacks pointed stare as he unlocked the door and the three rushed inside.
Seeing Captain Jack for the first time, Jackie smiled coyly at him and whispered to Mickey, "Who's he?"
Mickey grunted and walked to the Doctor. He offered his hand but the Doctor used it to pull Mickey into a hug, slapping his back twice before letting go.
"Didn't get to say hello properly, did we Ricky?" he explained, a mad grin on his face.
Jack coughed and the Doctors face returned to serious.
"We need to figure what the Daleks and the Sontarans are planning. Jack, you said they took Martha for some experiment?"
"Yeah, something that would change the face of humanity, and I'm quoting one of the Sontarans on this. Why?"
"Because, if the Daleks are here, aiding the Sontarans, maybe the "changing the face of humanity" thing might mean creating a new race of Daleks, Daleks evolved from human flesh and DNA."
"Is that possible?" Mickey asked, crossing his arms and staring at the Doctor.
"They did it before," Jack replied, answering before the Doctor could, "In the year 200100, the Daleks had created a new race… by using humans as their lab rats."
"And how did you stop 'em?" Mickey asked, staring at Rose, who has suddenly become still.
"…I did," she said, her eyes a-wash with tears, "I looked into the heart of the Tardis and used it to destroy the Dalek fleet… but… it," she stopped speaking, her voice crackling, heavy with tears.
"It was burning up her mind, so I took it out of her and into myself and returned it to the Tardis, but it killed me… which is how I became to look like this. I regenerated," The Doctor said, moving to the console and flipping switches. He set a scan for Dalek technology.
"But, Doctor, I don't understand. Why are the Sontarans working with the Daleks? What is in it for them?" Jack questioned, joining the Doctor at the console.
"The last time I faced the Sontarans, with Donna and Martha, they were trying to make the planet a cloning planet. If they still are planning to do that, the Daleks could aid in speeding up the process. But first, they get all of the human race to change into a new Dalek fleet. Both sides gain an advantage from the destruction of the Earth."
The Doctor faced Jack and, through clenched teeth, spoke in a whisper, "But I don't understand how Dalek Caan could do all of this by himself… He was the last surviving Dalek… he couldn't possibly do all this."
"So he found help from someone." Jack said, as if it was the most simple thing to say.
"Yes, but from whom?"
--
Dalek Caan laughed, his voice screeching as he giggled. His mind flew through great visions of water and fire, of spiders and beetles, of Time Lords and Daleks. He saw Skaro and Gallifrey burning, the Emperor failing; falling.
His mind was like a string, thinning and fraying and falling to pieces. He was open, feeling the bright light above him, which he doesn't remember being switched on, warming his skin. He reached a tentacle to it, feeling it as if like fire.
He flew and fell, the temporal shift sending him through time and space to what he'd ran away from in the first place.
He had broken through where so many others had failed and had found his creator, the last surviving Kaled.
And together, they had set about to change the universe, one planet at a time.