"Perception filter. Part of why it appears as a police box. It's stuck that way though. I mean stuck as a police box, not stuck with the perception filter on. Basically I didn't want them to see the TARDIS so they can't." After laying Evie down on the seat the Doctor started messing around at the consul. 

"It wasn't your suitcase. When I put the key next to the tracking device I set it up so the TARDIS would be at the last place I parked it. That being where I picked you up. I meant I was glad I left your bags because then I didn't have to worry about them, and they are here for you now." The Doctor was reading a screen as Nora asked how to stop the bad guys.

"That won't be easy. From what I understand they already have most of what they need to connect to the human system. It's a messy process. I haven't come across a group of them in a long time. They are called Torx. They feed and breed by hooking up to the nervous system of whatever race they're attacking. These guys that you've been talking to, they used to be human, but now the Torx is control. He has rewired the human and the only way of getting rid of it is to kill the human too. He can't live without the Torx. Think of them like zombies now, because that's all that is there." The Doctor turned to face Nora. She knew she would be taking this news well. 

There was a look of worry on her face. Could Nora handle this? Memories of her other companions flickered through her mind. How would Rose deal with this? Or Donna? Both would want to save the humans...how could he...she. How could she save the humans? Was there a way to reverse the process?