112 "I mean," explained Poirot, "you are sure it was bolted, and not merely locked?"
He felt the answer to his question would make all the difference in his theory of the murder. 
mnli hypothesis: He felt the answer to his question would make all the difference in his theory of the murder.  premise: 112 "I mean," explained Poirot, "you are sure it was bolted, and not merely locked?"