"F'r the love o' G.o.d," growled Ca.s.sidy, "is that YOU, Mr. Vaux!" He lowered his arms sheepishly, reached out and switched on the ceiling light over the dining-room table. "Well, f'r--" he began; and, seeing Miss Erith, subsided.

"What are you doing here?" demanded Vaux, disgusted with this glaring example of interference from another service.

"What am I doing?" repeated Ca.s.sidy with a sarcastic glance at Miss Erith. "Faith, I'm pinching a German gentleman we've been watching these three months and more. Is that what you're up to, too?"

"Herman Lauffer?"

"That's the lad, sir. He's in the kitchen yonder, dressing f'r to take a little walk. I gotta get his coat and vest. And what are you doing here, sir?"

"How did YOU get in?" asked Miss Erith, flushed with chagrin and disappointment.

"With keys, ma'am."

"Oh, Lord!" said Vaux, "we jimmied the door. What do you think of that, Ca.s.sidy?"

"Did you so?" grinned Ca.s.sidy, now secure in his triumphant priority and inclined to become friendly.

"I never dreamed that your division was watching Lauffer," continued Vaux, still red with vexation. "It's a wonder we didn't spoil the whole affair between us."

"It is that!" agreed Ca.s.sidy with a wider grin. "And you can take it from me, Mr. Vaux, we never knew that the Postal Inspection was on to this fellow at all at all until you called me to stop outgoing letters."

"What have you on him?" inquired Vaux.

Ca.s.sidy laughed:

"Oh, listen then! Would you believe this fellow was tryin' the old diagonal trick? Sure it was easy; I saw him mail a letter this afternoon and I got it. I'd been waiting three months for him to do something like that. But he's a fox--he is that, Mr. Vaux! Do you want to see the letter? I have it on me--"

He fished it out of his inside pocket and spread it on the dining table under the light.

"You know the game," he remarked, laying a thick forefinger on the diagonal line bisecting the page. "All I had to do was to test the letter by drawing that line across it from corner to corner. Read the words that the line cuts through. Can you beat it?"

Vaux and Miss Erith bent over the letter, read the apparently innocent message it contained, then read the words through which the diagonal line had been drawn.

Then Ca.s.sidy triumphantly read aloud the secret and treacherous information which the letter contained:

"SEVEN UNITED STATES TRANSPORTS TO-DAY NEW YORK (BY THE) NORTHERN ROUTE. INFORM OUR U-BOATS. URGENCY REQUIRES INSTANT MEASURES. TEN MORE ARE TO SAIL FROM HERE NEXT WEEK."

"The dirty Boche!" added Ca.s.sidy. "Dugan has left for Mexico to look up this brother of his and I'm lookin' up this snake, so I guess there's no harm done so far."

"New York.

"January 3rd. 1916.

"My dear Brother:

"For seven long weeks I have awaited a letter from you. The United-States mails from Mexico seem to be interrupted. Imagine my transports of joy when at last I hear from you today. You and I, dear brother, are the only ones left of our family--you in Vera Cruz. I in New-York--you in a hot Southern climate, I in a Northern, amid snow and ice, where the tardy sun does not route me from my bed till late in the morning.

"However, I inform you with pleasure that I am well. I rejoice that our good health is mutual. After all, the dear old U. S. suits me.

Of course railroads or boats could carry me to a warm climate, in case urgency required it. But I am quite well now, and my health requires merely prudence. However, if I am again ill at any instant, I shall leave for Florida, where all tho proper measures can be taken to combat my rheumatism,

"Ten days ago I was in bed, and unable to do more than move my left arm. But the doctors are confident that my malady is not going to return. If it does threaten to return I shall sail for Jacksonville at once, and from there go to Miami, and not return here until the warm and balmy weather of next spring has lasted at least a week.

Affectionataly your brother.

"Herman."

He pocketed the letter and went into the bedroom to get a coat and vest for the prisoner. Miss Erith looked at Vaux.

"Ca.s.sidy seems to know nothing about the code-cipher," she whispered. "I think he rummaged on general principles, not in search of any code-book."

She looked around the dining-room. The doors of the yellow oak sideboard were open, but no book was there among the plated knives and forks and the cheap dishes.

Ca.s.sidy came back with the garments he had been looking for--an overcoat, coat and vest--and he carried them into the kitchenette, whither presently Vaux followed him.

Ca.s.sidy had just unlocked the handcuffs from the powerful wrists of a dark, stocky, sullen man who stood in his shirt-sleeves near a small deal table.

"Lauffer?" inquired Vaux, dryly.

"It sure is, ain't it, Herman?" replied Ca.s.sidy facetiously. "Now, then, me Dutch bucko, climb into your jeans, if YOU please--there's a good little Boche!"

Vaux gazed curiously at the spy, who returned his inspection coolly enough while he wrinkled his nose at him, and his beady eyes roamed over him.

When the prisoner had b.u.t.toned his vest and coat, Ca.s.sidy snapped on the bracelets again, whistling cheerily under his breath.

As they started to leave the kitchenette, Vaux, who brought up the rear, caught sight of a large, thick book lying on the pantry shelf.

It was labelled "Perfect Cook-Book," but he picked it up, shoved it into his overcoat pocket en pa.s.sant, and followed Ca.s.sidy and his prisoner into the dining-room.

Here Ca.s.sidy turned humorously to him and to Miss Erith.

"I've cleaned up the place," he remarked, "but you're welcome to stay here and rummage if you want to. I'm sending one of our men back to take possession as soon as I lock up this bird."

"All right. Good luck," nodded Vaux.

Ca.s.sidy tipped his derby to Miss Erith, bestowed a friendly grin on Vaux.

"Come along, old sport!" he said genially to Lauffer; and he walked away with his handcuffed prisoner, whistling "Garryowen."

"Wait!" motioned Vaux to Miss Erith. He went to the stairs, listened to the progress of agent and prey, heard the street-door clash, then hastened back to the lighted dining-room, pulling the "Perfect Cook-Book" from his pocket.

"I found that in the kitchenette," he remarked, laying it before her on the table. "Maybe that's the key?"

"A cook-book!" She smiled, opened it. "Why--why, it's a DICTIONARY!" she exclaimed excitedly.

"A dictionary!"

"Yes! Look! Stormonth's English Dictionary!"

"By ginger!" he said. "I believe it's the code-book! Where is your cipher letter, Miss Erith!"

The girl produced it with hands that trembled a trifle, spread it out under the light. Then she drew from her pocket a little pad and a pencil.