Based from the episode 'Bad Wolf', series 1, ep 12
2.
The Doctor watched Jack wire the extrapolator to the defence system, manipulating the wires, ignoring the commotion around him. He wondered if he should take the watch from him, bring him back. Two heads were better than one. But there was no telling who Jack had been before, or even how far along his training had been in the academy, what regeneration he was on, if any. Too much risk. It hurt, though. They were going to die. The Delta Wave would never be reformed in time to save anyone's life. He was going to make that painful decision to kill his race again, and kill humankind into the bargain. At least he knew that someone had survived, if even for a short while. Now he was going to die, with the last of his kind, and they didn't even know it.
Rose worked on stripping the wires, giving it her all, trying not to mess up. She believed they would get through it. Such beautiful hope the human race had. It almost made you forget they were stupid little apes that could barely walk without falling. They were a shining beacon, an amazing race that grew and grew and lived on and on no matter what the hardship.
Jack turned to the others in the area, explaining the situation. Lying. Bullets would never make it through their shields. The eye stalk was their only hope, and one bullet in two thousand would strike. Jack was already making out to be a good Time Lord. False hope, when there was none. Inspiring, charismatic, manipulative. Just like him. He fiddled with the main console, adjusting frequencies with his sonic.
He looked back at Rose, the innocent soul that had pulled him from the brink. Fifty years had been such a long time alone. He let out a long breath.
If he couldn't rely on the wave, he had to fulfill his promise to Jackie. Rose wasn't going to like it.
He glanced up when he felt eyes on him. Jack was watching him.
For all the glamour, all the flirting, and the air-head act, there was more to Jack. He was dangerous, a con man, a man who'd stop at nothing to get the job done, no matter the cost. He was also perceptive. He saw more of him than he'd care to admit.
Jack stepped closer to the Doctor. "Save her," he said. "If you can."
The Doctor nodded. "I promise."
Jack started to turn away, but the Doctor stopped him with a hand on his arm.
"When this is over, if we survive," said the Doctor, trying to let out an easy breath, "I have something important to discuss."
Jack grinned, but it didn't touch his eyes. He was worried. "Alright."
"For now, just trust me," said the Doctor.
"Always," said Jack.