Who said it?

"They were peaceable; they gave no argument. When we questioned them, all they would say was  'Ying Ko' -- and they kept repeating it. Sounded like a name; but there's nobody in Chinatown with that moniker. It's not a place, either -- I've looked through atlases trying to find it. 'Ying Ko' -- that's all they would say."

The issue that this quote came from is the first time that Ying Ko is mentioned.  Who said the above quote and what adventure did it come from?