"I'm the Doctor. And I presume that you are the Winchesters? And Castiel, of course."
*** 3 days earlier ***
"Dean, are you sure that this is our kind of thing?"
"Cas seems to think it is. And there's no way it's not something supernatural. I mean, it's not like it could just be rolling away while no one's looking. People have actually seen it disappearing."
"Dean. It's a box."
"Your point?"
"Don't we have demons to kill? A disappearing blue box isn't exactly top priority."
"Sam, that's the thing. This is our only case in weeks."
"Fine. Let's go chase a magic blue box."