"An alien signal, yeah." The Doctor replied to the girls surprised reaction, continuing to scan around the corridor with his sonic, his thin figure twisting around like a bendy ruler. "Oh, what's this thing? This, is my sonic screwdriver. If you need to open a locked door or detect something strange, this is your gadget." 

Suddenly, The Time Lords old eyes focused directly behind the girl, as the sonic screwdriver began to bleep faster and faster. He took a few steps forward, before he lowered his hands down back to his side, not keeping his eyes from further down the corridor. He looked as if he had seen a ghost. 

"Well, this is...bad." The Doctor commented. Stood behind the young girl, was what looked like the night guard. A big, muscular and tattooed individual with a threatening look in his dark green eyes as he seemed to glare menacingly at the Doctor. 

"Hey," The Doctor indicated to the young girl in front of him, holding up his hand slowly as if for her to take. "Come slowly to me." The whole time, he never let his vision leave the 'night guard.'