As the Doctor and Martha gaped, Jack began changing.
"What?" was all the Doctor could say.
Jack had turned into a tall man with a suit, bowtie, high cheek bones, blond hair, and blue eyes.
"What?"
"Your flattering me, Doctor. How have you been? Oh, yes, that's right, you don't know me. It's just I've been following you so long…"
It looked around.
"What? You haven't felt my presence? Shame, Doctor. I caused you to meet Rose."
It looked at Martha.
"He didn't tell you? Shame, Doctor. I guess you cant bear to remember your companions once you leave them. Say, what happened to Ace?"
The Doctor finally found his voice
"Who are you?"
"Well, Time Lord form Galifrey," the Doctor gaped, "you could call me a Shadow. The Shadow, or John Barrowman. Either way I'm Captain Jack Harkness." he said as he melted back into Jacks form.
"Wrong question. What are you?"
"I am a being from another universe who can copy or steal any power, manipulate energy in any form, control the elements in any form, and can control shadows. Including Vashta Nerada. My name is John Barrowman, though not the actor."
He ran regeneration energy across his fingers.
"I got this from a Time Lord who stumbled into my universe. Very chatty and cooperative. Prattled about not wanting to be a Time Lord. I told him I would make him human if he gave me his regenerations. Gave them willingly.
It flashed a smile.
The Doctor was shaking his head.
"You claim to have so much power. Why spend time with me?"
"You are so fascinating, Doctor. You are the only creature I have encountered that can single-handedly save the universe. You have legions of people who love you, but they don't know your name."
It looked at the Doctor.
"How could you do that, Doctor? Trillions love you, and not just in this universe. What is so dangerous about your name? Not even I know. WHAT THE HELL IS SO IMPORTANT ABOUT YOUR NAME?" Its shouts shook the TARDIS.
The Doctor responded angrily, "I take complete strangers onboard my TARDIS and let them live here! I think I deserve one secret!"
"One secret, Doctor? You are the most secretive person I have ever watched. Wont tell your name, won't talk about the War, won't even talk about your life on Galifrey! Why?"