The Doctor stepped cautiously into the cellar, sonic screwdriver at the ready. He did not know what he was going to find, or what he wasn't going to find. He hoped he would find her, preferably alive, but he also hoped he would not. Something terrible had happened in that house. He feared for the worst.
The cellar was too dark to see anything clearly, and the Doctor couldn't seem to find a light of any kind. This was a modern home, shouldn't there be a light switch or something? He felt the walls, his palms scanning for anything. He found a button, but upon pressing it he found that nothing happened. He turned on his sonic screwdriver, and the tiny light it emitted gave him a good enough view of his surroundings to find the light switch, directly opposite of the wall he had been searching. He flicked it on, and the cellar was immediately lit. He then realized it was much more than a cellar. It was a series of catacombs, woven together intricately.
The Doctor loved a good mystery, but this made him nervous. This wasn't right. He could feel that something dangerous was here. Lurking. Waiting for him to happen upon it. He grasped his sonic screwdriver tightly, prepared for anything. He proceeded down the corridor, not quite sure where he was going, but following his instinct had worked for him in the past.
He walked for what felt like hours, going down one staircase, then two, then three. Through one door, then two, then six, then eleven, he was losing count. He wandered along, wondering if maybe the note had been placed there to lead him in the wrong direction. It would be like him to fall for something like that. But just when he had finally lost hope, a door burst open.
She dashed out, closing the door behind her.
"Oh, uh, hello." She breathed with a smile. "Long time no see. I'm rather in a hurry right now, and you should probably run, that would be-" her body swayed. The Doctor stepped closer, concerned. "That would be...fantastic..." she whispered and her body crumpled. The Doctor reached out, catching her, saving her from the fall. The door opened.
Donna Noble stepped out.
But then she shuddered, and she wasn't Donna Noble anymore.
Mickey Smith was standing there.
But then he shuddered, and he wasn't Mickey Smith anymore.
This happened several times, shifting from Doctor Constantine to Reinette Poisson to a Weeping Angel to Rory Williams and finally settling on Captain Jack Harkness.
"Sorry." Jack said with a grin. "I had to find the right form."

They sat inside the room. The Doctor sat on the floor, she was laid on the floor next to the Doctor, and Jack sat in the only chair in the room, smoking a cigarette.
"What are you?" The Doctor asked bluntly. He was very confused.
"I'm the Grunge."
"How can you take so many forms without ever having formed a psychic link?"
"I'm not taking any forms. Everyone sees us differently. What you are seeing is an image created by your own mind."
"So you're not shape shifters?"
"No. We are living mind games."
"Why did you come here?"
"Our home planet was destroyed many years ago, but they had appropriate resources to sustain our race."
"So you're not harming anyone. Just looking for a place to live?"
"Well, we haven't harmed anyone yet."
"Yet?"
He motioned to her.
"Why?" The Doctor asked, feeling protective. "Who is she to you?"
"Who is she? Well, she's the girl that time forgot."