"When was that?"
"Yesterday afternoon," replied the director. "Every now and then—at irregular intervals—we weigh all the gold in the Mint, to make sure that everything is as it should be. Nothing wrong was discovered until we reached Vault Six, but there fifty bars were missing. There wasn't any chance of error. The records showed precisely how much should have been there and the scales showed how much there was, to the fraction of an ounce.
"But even if we had only counted the bars, instead of weighing each one separately, the theft would have been instantly discovered, for the vault contained exactly fifty bars less than it should have. It was then that I wired Washington and asked for assistance from the Secret Service."
"Thus spoiling my vacation," muttered Drummond. "How many men know the combination to the vault door?"
"Only two," replied the superintendent. "Cochrane, who is the official weigher, and myself. Cochrane is above suspicion. He's been here for the past thirty years and there hasn't been a single complaint against him in all that time."
Drummond looked as if he would like to ask Preston if the same could be said for the superintendent, but he contented himself with listening as Bosbyshell continued:
"But even if Cochrane or I—yes, I'm just as much to be suspected as he—could have managed to open the vault door unseen, we could not have gotten inside the iron grille which guards the gold in the interior of the vault. That is always kept locked, with a combination known to two other men only. There's too much gold in each one of these vaults to take any chance with, which is the reason for this double protection. Two men—Cochrane and I—handle the combination to the vault door and open it whenever necessary. Two others—Jamison and Strubel—are the only ones that know how to open the grille door. One of them has to be present whenever the bars are put in or taken away, for the men who can get inside the vault cannot enter the grille, and the men who can manipulate the grille door can't get into the vault."
"It certainly sounds like a burglar-proof combination," commented Drummond. "Is there any possibility for conspiracy between"—and he hesitated for the fraction of a second—"between Cochrane and either of the men who can open the grille door?"
"Apparently not the least in the world," replied Preston. "So far as we know they are all as honest as the day—"
"But the fact remains," Drummond interrupted, "that the gold is missing."