Take the following as truth: It's nothing much, but ”well, if you are going, will you tell him ” he dropped his voice to a whisper ”"I think I've found the extra coffee-cup!" I had almost forgotten that enigmatical message of Poirot's, but now my curiosity was aroused afresh. 
Then the following statement: "His voice was casual, but also careful and wary, when he told me that he had found the extra coffee cup." is true, false, or inconclusive?
Answer: True