"That is all, Mason."
"Yes, sir."
The moment the door closed behind the old butler McKelvie said, with a smile, "Just as I thought. And what came in handy when his father was alive was doubly useful after his marriage. And thus we come back to the original discussion, whether the criminal would know the three necessary facts to enter by the safe."
"A member of the family might," I said.
"Yes, a member of the family. Lee, for instance, or even Orton might discover that there was such a passage and secure a key to it. Would either of them know the combination?"
"Orton was Darwin's private secretary."
"As far as his business down-town went, but not his secretary, as far as his personal affairs were concerned. Besides, recall Mason's testimony. He was surprised to find Orton in the study because Darwin always kept it religiously locked, to preserve his secret, of course. Then, too, Orton was Darwin's creature and, therefore, he would be doubly careful not to place himself in the fellow's power. He evidently considered he was running no risk, since he let Orton into the study that night. Besides, if you did not want anyone prying into your safe, what precaution would you take to prevent it?"
"I'd change the combination frequently."
"Exactly; and there you have an answer to my problem. Granted that the criminal knew the first two facts, was he going to depend on a combination that might be changed five minutes before he wished to use the entrance? No, no, we're dealing with a person too clever not to foresee that contingency. Besides, as far as I could detect, no one has recently taken an impression of the outer lock."
"Then we get back where we started and the entrance is of no value to us at all," I pointed out.