Nick was an expert chirographist.  To have deceived him with a disguised handwriting would have been utterly impossible, and none knew it better than Chick, who now nodded approvingly.

“Some outside party, eh?”

“There is no doubt of it, Chick.  And this conclusion at once suggests two very natural questions,” Nick went on.  “First, was one of the Kilgore gang in Hafferman’s store when Venner went there yesterday, and did he overhear enough of what passed between them to enable him to plan the job done this morning?”

“Possibly.”

“In opposition to that theory, however, is the fact that the forged order is written on one of Venner’s printed letter sheets.”

“By a little adroit work, Nick, one of the gang could have obtained a sheet of Venner’s office paper.”

“That is very true,” admitted Nick.  “But since this is a theory founded only upon conjecture, with no positive evidence to back it up, the stronger probability is rather to the contrary.”

“Right, Nick, as far as that goes.”

“I think so.”

“And what is the second theory suggested?”

“That some clerk in one of the stores got wind of Venner’s contemplated purchase, and revealed the fact to one of the Kilgore gang, by whom I am confident—­bear in mind—­that the crime was committed.”

“That theory seems plausible,” nodded Chick.  “There is young Boyden, you know, at Hafferman’s.  He may have got wise to Venner’s intentions.  Garside remarked that he appeared quite anxious to leave the diamonds until Venner should return.  That would have been very natural on his part, in case he was then co-operating with the party who finally secured them.”

“The same objection again arises, however,” argued Nick.  “Boyden is not employed at Venner’s, and therefore has not access to his letter paper.  Furthermore, Venner’s visit was made only yesterday afternoon, less than twenty-four hours before the robbery occurred.  It seems hardly probable that Boyden was already in league with the Kilgore gang; and, if he was not, it is even less probable that he so quickly got in touch with them.”

“By Jove! that’s so,” cried Chick.  “As a matter of fact, then, neither of these theories has a reliable leg to stand upon.”

“That’s exactly my conclusion,” laughed Nick.

“And what then?”

“Concerning that side of the affair,” replied Nick, “several irresistible convictions are therefore forced upon me.  One of the Kilgore gang certainly knew of Venner’s visit, and of the request he made Hafferman regarding the diamonds.  Otherwise he could not have planned the job so neatly.  Somebody must have informed him.  Somebody must have provided him with one of Venner’s letter sheets.  If we eliminate the clerks, and the members of both firms, we are left very much in the dark.”

“I should say so,” rejoined Chick.  “The affair becomes a dense mystery.”