The TARDIS groaned to a halt down a London back alley. No one would see it there, he thought. Humans could barely tell when the sun was up. The Doctor stepped out of the blue doors and brushed the dust accumulated from so many years of fighting from his leather jacket, and ran a hand through his hair, or at least he would have, if he still had hair. He hadn't quite gotten used to that aspect of his new head just yet. He took a deep breath of the thick city air and set off on his way.
"Alright, sonic screwdriver? Check. Psychic paper? Check. TARDIS key?"
He pats his pockets for a moment
"Check."
The Doctor had come to Earth for a reason this time, not just for the memories. He had heard a rumor a few solar systems over that a migrating herd of Cadullons had found their way onto the planet and were causing a bit of trouble. Cadullons are a gregarious interstellar species that resemble vultures, except for being about 10 centimeters long and being coloured a very curious shade of moderately invisible lime green. Now normally a small flock of an avian species such as this wouldn't be much of a problem, Cadullons, however, tend to flock in numbers approaching a thousand, and are fond of consuming Silicon Dioxide, commonly known on Earth as glass, which could pose a problem in a city with buildings largely constructed of glass. A city like London.
Then he heard it, the very distinct sound of a Cadullon call, much like the sound of small wind chimes. The Doctor quickly scanned the sky above him and there he saw them, a small group of the things, numbering about 786 if he had to guess. They were circling around a nearby sky scraper, and every once in a while, one would swoop in and peck at the glass of the upper floors. He sped off in the direction of the building and when he got there he was quite relieved to see that it still under construction, as men were moving furniture into the first floor area, what looked like the buildings main lobby. He made his way to the door when he was stopped by a voice from behind
"Oi you, can't go in there, private property"
The Doctor spun around to find a small balding construction worker looking at him, he reached into a coat pocket and pulled out the psychic paper, showing it to the man
"City of London Building Inspector Brigade, now if you'll excuse me I-"
"We didn't hear nothin' about any inspection goin' on"
"Listen, this is important so if I could just get inside, just need to have a little poke around, nothing to worry about. Tell you what: you let me go through, and I'll put in a good word for you back at Headquarters"
"Well..." he hesitates "alright. Don't go breaking anything"
The Doctor gave a grin
"Wouldn't dream of it"
He maneuvered through the small crowd of mover men to the stairs and started climbing his way up