"If you want to find missin' vampires, you're gonna need to think like one. I'm coming with you." The way he says it, with finality, makes it clear that's that. No room for argument or debate. Maybe this is all just an elaborate trap. Send the doctor out as bait and lure him in with a sob story about missing vampire. Well, if it is a trap, it's working. He'll just have to keep his guard up until he's sure of what's going on.

"Is Islington territory the only place you've checked?" It'll just waste time to cover territory Morgan has already gone through.