Suspicion weakens in the presence of incongruity.
"This fellow seems less than half-witted," I said, "but he's shrewd, and I've found him useful.

Unfortunately he has picked up a lot of information, so we'll have to keep an eye on him.

My business is to communicate with the French General Staff and I'm told you know how to manage it." "Huh-huh?
Who told you that ?" "Those who gave me my instructions.

If you don't know who they are without my telling you, you're the wrong man and I'll not waste time with you." "Let us suppose that I know then.

Proceed." "Your name was given to me as that of a man who can be trusted to take necessary action in the interests of ...