"At my suggestion they made a careful examination into the private lives of all employees of the post-office, including myself," Rogers answered, a bit pompously. "I did not intend to evade the slightest responsibility in the matter, so I turned over my bankbook, the key to my safe-deposit vault and even allowed them to search my house from cellar to garret."

"Was this procedure followed with respect to all the other employees in the building?"

"No, only one or two of the highest--personal friends of mine whom I could trust to keep silent. I didn't care to swear out search warrants for the residences of all the people who work here, and that's what it would have meant if they had raised any objection. In their cases the investigation was confined to inquiries concerning their expenditures in the neighborhood, unexpected prosperity, and the like."

"With what result?"

"None at all. From all appearances there isn't a soul in this building who has had ten cents more during the past six weeks than he possessed in any like period for two years back."

"Did Boyd or any of the other department operatives ask to see the plans of the post office?" inquired Allison, taking another tack.

"The what?"

"The plans of the post-office--the blue print prepared at the time that the building was erected."

"No. Why should they?"

"I thought they might have been interested in it, that's all," was Allison's answer, but anyone who knew him would have noted that his tone was just a trifle too nonchalant to be entirely truthful.

"By the way," added the operative, "might I see it?"

"The blue print?"

"Yes. You will probably find it in the safe. If you'll have some one look it up, I'll be back in half an hour to examine it," said Allison.

"Meanwhile, I'll talk to Boyd and the other men already on the ground and see if I can dig anything out of what they've discovered."

But Boyd and his a.s.sociates were just as relieved as Rogers had been to find that the case had been placed in Allison's hands. Four weeks and more of steady work had left them precisely where they had commenced--"several miles back of that point," as one of them admitted, "for three more stunts have been pulled off right under our eyes." The personal as well as the official record of every man and woman in the Columbus post office had been gone over with a microscope, without the slightest result. If the germ of dishonesty was present, it was certainly well hidden.

"We'll try another and more powerful lens," Allison stated, as he turned back to the postmaster's private office. "By the way, Boyd, have you or any of your men been in the Service more than four years?"

"No, I don't think any of us has. What has that got to do with it?"

"Not a thing in the world, as far as your ability is concerned, but there is one point that every one of you overlooked--because you never heard of it. I'm going to try it out myself now and I'll let you know what develops."

With that Allison turned and sauntered back into Rogers's office.

There, spread upon the desk, was the missing blue print, creased and dusty from disuse.

"First time you ever saw this, eh?" Allison inquired of the postmaster.

"The first time I even knew it was there," admitted that official.

"How'd you know where to find it?"

"I didn't--but there's an ironclad rule of the department that plans of this nature are to be kept under lock and key for just such emergencies as this. But I guess your predecessor was too busy to worry you with details."

Rogers grunted. It was an open secret that the postmaster who had preceded him had not been any too friendly to his successor.

Allison did not pursue the subject but spread the plan upon an unoccupied table so that he could examine it with care.

"If you'll be good enough to lock that door, Postmaster," he directed, "I'll show you something else about your building that you didn't know.

But I don't want anybody else coming in while we're discussing it."

Puzzled, but feeling that the government detective ought to be allowed to handle things in his own way, Rogers turned the key in the lock and came over to the table where Allison stood.

"Do you see that little square marked with a white star and the letter 'L'?" asked Elmer.

"Yes, what is it?"

"What is this large room next to it?" countered the operative.

"That's the--why, that's the registry room!"

"Precisely. And concealed in the wall in a spot known only to persons familiar with this blue print, is a tiny closet, or 'lookout.' That's what the 'L' means and that's the reason that there's a strict rule about guarding plans of this nature very carefully."

"You mean to say that a place has been provided for supervision of the registry division--a room from which the clerks can be watched without their knowledge?"

"Exactly--and such a precaution has been taken in practically every post office of any size in the country. Only the older men in the Service know about it, which is the reason that neither Boyd nor any of his men asked to see this set of plans. The next step is to find the key to the lookout and start in on a very monotonous spell of watchful waiting. You have the bunch of master keys, of course?"

"Yes, they're in the safe where the plans were kept. Just a moment and I'll get them."

When Rogers produced the collection of keys, Allison ran hurriedly over them and selected one which bore, on the handle, a small six-pointed star corresponding to the mark on the blue print.

"Want to go up with me and investigate the secret chamber?" he inquired.

"I certainly do," agreed Rogers. "But there's one point where this room won't help us in the slightest. How did the thief get the mail containing the money out of the building? You know the system that maintains in the registry room? It's practically impossible for a sheet of paper to be taken out of there, particularly when we are on guard, as we are now."

"That's true," Allison admitted, "but it's been my experience that problems which appear the most puzzling are, after all, the simplest of explanation. You remember the Philadelphia mint robbery--the one that Drummond solved in less than six hours? This may prove to be just as easy."

There Allison was wrong, dead wrong--as he had to admit some ten days later, when, worn with the strain of sitting for hours at a time with his eyes glued to the ventilator which masked the opening to the lookout, he finally came to the conclusion that something would have to be done to speed things up. It was true that no new robberies had occurred in the meantime, but neither had any of the old ones been punished. The lost one hundred thousand dollars was still lost; though the department, with the aid of the Treasury officials, had seen that the banks were reimbursed.

"The decoy letter," thought Allison, "is probably the oldest dodge in the world. But, who knows, it may work again in this case--provided we stage-manage it sufficiently carefully."

With the a.s.sistance of the cashier of one of the local banks Elmer arranged to have a dummy package of money forwarded by mail from New York. It was supposed to contain thirty-five thousand dollars in cash, and all the formalities were complied with precisely as if thirty-five thousand-dollar bills were really inside the envelope, instead of as many sheets of blank paper carefully arranged.

On the morning of the day the envelope was due to reach Columbus, Allison took up his position close to the grille in the lookout, his eyes strained to catch the slightest suspicious movement below. Hour after hour pa.s.sed uneventfully until, almost immediately below him, he saw a man drop something on the floor. Two envelopes had slipped from his hands and he stooped to pick them up--that was all.

But what carried a thrill to the operative in the lookout was the fact that one of the envelopes was the dummy sent from New York and that, when the man straightened up, he had only _one_ of the two in his hands.

The dummy had disappeared!

Allison rubbed his eyes and looked again. No, he was right. The postal clerk had, in some manner, disposed of the envelope supposed to contain thirty-five thousand dollars and he was going about his work in precisely the same way as before.

"Wait a minute," Allison argued to himself. "There's something missing besides the envelope! What is it?"

A moment later he had the clue to the whole affair--the jaws of the clerk, which Allison had previously and subconsciously noted were always hard at work on a wad of gum, now were at rest for the first time since the operative had entered the lookout! The chewing gum and the dummy packet had disappeared at the same time!

It didn't take Elmer more than thirty seconds to reach Rogers's office, and he entered with the startling announcement that "an envelope containing thirty-five thousand dollars had just disappeared from the registry room."

"What?" demanded the postmaster. "How do you know? I haven't received any report of it."