"Somewhat. It involves almost anything short of life imprisonment.

But I don't mind."

"We couldn't get a search-warrant, could we?"

"We have found nothing, so far, in that cipher letter to encourage us in applying for any such warrant," he said cruelly.

"Wouldn't the excuse that Lauffer is an enemy alien and not registered aid us in securing a warrant?" she insisted.

"He is not an alien. I investigated that after you left this afternoon. His parents were German but he was born in Chicago. However, he is a Hun, all right—I don't doubt that…. What do you propose to do now?"

She looked at him appealingly:

"Won't you allow me more than twenty-four hours?"

"I'm sorry."

"Why won't you?"

"Because I can't dawdle over this affair."

The girl smiled at him in her attractive, resolute way:

"Unless we find that book we can't decipher this letter. The letter comes from Mexico,—from that German-infested Republic. It is written to a man of German parentage and it is written in cipher. The names of Luxburg, Caillaux, Bolo, Bernstorff are still fresh in our minds. Every day brings us word of some new attempt at sabotage in the United States. Isn't there ANY way, Mr. Vaux, for us to secure the key to this cipher letter?"

"Not unless we go up and knock this man Lauffer on the head. Do you want to try it?"

"Couldn't we knock rather gently on his head?"

Vaux stifled a laugh. The girl was so pretty, the risk so tremendous, the entire proceeding so utterly outrageous that a delightful sense of exhilaration possessed him.

"Where's that gun?" he said.

She drew it out and handed it to him.

"Is it loaded?"

"Yes."

"Where are the handcuffs?"

She fished out the nickel-plated bracelets and he pocketed his torch. A pleasant thrill passed through the rather ethereal anatomy of Mr. Vaux.

"All right," he said briskly. "Here's hoping for adjoining cells!"

To jimmy the glass door was the swiftly cautious work of a moment or two. Then the dark stairs rose in front of them and Vaux took the lead. It was as cold as the pole in there, but Vaux's blood was racing now. And alas! the photograph of Arethusa was in his desk at the office!

On the third floor he flashed his torch through an empty corridor and played it smartly over every closed door. On the fourth floor he took his torch in his left hand, his pistol in his right.

"The door to the apartment is open!" she whispered.

It was. A lamp on a table inside was still burning. They had a glimpse of a cheap carpet on the floor, cheap and gaudy furniture. Vaux extinguished and pocketed his torch, then, pistol lifted, he stepped noiselessly into the front room.

It seemed to be a sort of sitting-room, and was in disorder; cushions from a lounge lay about the floor; several books were scattered near them; an upholstered chair had been ripped open and disembowelled, and its excelsior stuffing strewn broadcast.

"This place looks as though it had been robbed!" whispered Vaux.

"What the deuce do you suppose has happened?"

They moved cautiously to the connecting-door of the room in the rear. The lamplight partly illuminated it, revealing it as a bedroom.

Bedclothes trailed to the floor, which also was littered with dingy masculine apparel flung about at random. Pockets of trousers and of coats had been turned inside out, in what apparently had been a hasty and frantic search.

The remainder of the room was in disorder, too; underwear had been pulled from dresser and bureau; the built-in wardrobe doors swung ajar and the clothing lay scattered about, every pocket turned inside out.

"For heaven's sake," muttered Vaux, "what do you suppose this means?"

"Look!" she whispered, clutching his arm and pointing to the fireplace at their feet.

On the white-tiled hearth in front of the unlighted gas-logs lay the stump of a cigar.

From it curled a thin thread of smoke.

They stared at the smoking stub on the hearth, gazed fearfully around the dimly lighted bedroom, and peered into the dark dining-room beyond.

Suddenly Miss Erith's hand tightened on his sleeve.

"Hark!" she motioned.

He heard it, too—a scuffling noise of heavy feet behind a closed door somewhere beyond the darkened dining-room.

"There's somebody in the kitchenette!" she whispered.

Vaux produced his pistol; they stole forward into the dining-room; halted by the table.

"Flash that door," he said in a low voice.

Her electric torch played over the closed kitchen door for an instant, then, at a whispered word from him, she shut it off and the dining-room was plunged again into darkness.

And then, before Vaux or Miss Erith had concluded what next was to be done, the kitchen door opened; and, against the dangling lighted bulb within, loomed a burly figure wearing hat and overcoat and a big bass voice rumbled through the apartment:

"All right, all right, keep your shirt on and I'll get your coat and vest for you—"

Then Miss Erith flashed her torch full in the man's face, blinding him. And Vaux covered him with levelled pistol.

Even then the man made a swift motion toward his pocket, but at Vaux's briskly cheerful warning he checked himself and sullenly and very slowly raised both empty hands.

"All right, all right," he grumbled. "It's on me this time. Go on; what's the idea?"

"W-well, upon my word!" stammered Vaux, "it's Cassidy!"

"F'r the love o' God," growled Cassidy, "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 Cassidy 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, Cassidy?"

"Did you so?" grinned Cassidy, 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 Cassidy 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.

Cassidy 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 Cassidy 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 Cassidy. "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.

"Cassidy 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.

Cassidy 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.

Cassidy 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 Cassidy 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 buttoned his vest and coat, Cassidy 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 passant, and followed Cassidy and his prisoner into the dining-room.

Here Cassidy 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.

Cassidy 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.

"Quick," she said, "look for page 17!"

"Yes, I have it!"

"First column!"

"Yes."

"Now try the twentieth word from the top!"

He counted downward very carefully.

"It is the word 'anagraph,'" he said; and she wrote it down.

"Also, we had better try the twentieth word counting from the bottom of the page up," she said. "It might possibly be that."

"The twentieth word, counting from the bottom of the column upward, is the word 'an,'" he said. She wrote it.

"Now," she continued, "try page 15, second column, third word from TOP!"

"'Ambrosia' is the word."

"Try the third word from the BOTTOM."

"'American.'"

She pointed to the four words which she had written. Counting from the TOP of the page downward the first two words were "Anagraph ambrosia." But counting from the BOTTOM upward the two words formed the phrase: "AN AMERICAN."

"Try page 730, first column, seventh word from the bottom," she said, controlling her excitement with an effort.

"The word is 'who.'"

"Page 212, second column, first word!"

"'For.'"

"Page 507, first column, seventh word!"

"'Reasons.'"

"We have the key!" she exclaimed. "Look at what I've written!—'An American who for reasons!' And here, in the cipher letter, it goes on—'of the most'—Do you see?"

"It certainly looks like the key," he said. "But we'd better try another word or two."

"Try page 717, first column, ninth word."

"The word is 'vital.'"

"Page 274, second column, second word."

"'Importance!'"

"It is the key! Here is what I have written: 'An American who for reasons, of the most vital importance!' Quick. We don't want a Secret Service man to find us here, Mr. Vaux! He'd object to our removing this book from Lauffer's apartment. Put it into your pocket and run!" And the pretty Miss Erith turned and took to her heels with Vaux after her.

Through the disordered apartment and down the stairs they sped, out into the icy darkness and around the corner, where her car stood, engine running, and a blanket over the hood.

As soon as the chauffeur espied them he whisked off the blanket;

Miss Erith said: "Home!" and jumped in, and Vaux followed.

Deep under the fur robe they burrowed, shivering more from sheer excitement than from cold, and the car flew across to Fifth Avenue and then northward along deserted sidewalks and a wintry park, where naked trees and shrubs stood stark as iron in the lustre of the white electric lamps.

"That time the Secret Service made a mess of it," he said with a nervous laugh. "Did you notice Cassidy's grin of triumph?"

"Poor Cassidy," she said.

"I don't know. He butted in."

"All the services are working at cross-purposes. It's a pity."

"Well, Cassidy got his man. That's practically all he came for. Evidently he never heard of a code-book in connection with Lauffer's activities. That diagonal cipher caught him."

"What luck," she murmured, "that you noticed that cook-book in the pantry! And what common sense you displayed in smuggling it!"

"I didn't suppose it was THE book; I just took a chance."

"To take a chance is the best way to make good, isn't it?" she said, laughing. "Oh, I am so thrilled, Mr. Vaux! I shall sit up all night over my darling cipher and my fascinating code-book-dictionary."

"Will you be down in the morning?" he inquired.

"Of course. Then to-morrow evening, if you will come to my house, I shall expect to show you the entire letter neatly deciphered."

"Fine!" he exclaimed as the car stopped before her door.

She insisted on sending him home in her car, and he was very grateful; so when he had seen her safely inside her house with the cook-book-dictionary clasped in her arms and a most enchanting smile on her pretty face, he made his adieux, descended the steps, and her car whirled him swiftly homeward through the arctic night.