Tommy and Tuppence were closeted with the Chief in his private room. His commendation had been warm and sincere.

"You have succeeded admirably. Thanks to you we have laid our hands on no less than five very interesting personages, and from them we have received much valuable information. Meanwhile I learn from a creditable source that headquarters in Moscow have taken alarm at the failure of their agents to report. I think, that in spite of all our precautions, they have begun to suspect that all is not well at what I may call the distributing centre-the office of Mr. Theodore Blunt-the International Detective Bureau."

"Well," said Tommy. "I suppose they were bound to tumble to it sometime or other, sir."

"As you say, it was only to be expected. But I am a little worried-about Mrs. Tommy."

"I can look after her all right, sir," said Tommy, at exactly the same minute as Tuppence said, "I can take care of myself."

"H'm," said Mr. Carter. "Excessive self-confidence was always a characteristic of you two. Whether your immunity is entirely due to your own superhuman cleverness, or whether a small percentage of luck creeps in, I'm not prepared to say. But luck changes, you know. However, I won't argue the point. From my extensive knowledge of Mrs. Tommy, I suppose it's quite useless to ask her to keep out of the limelight for the next week or two?"

Tuppence shook her head very energetically.

"Then all I can do is to give you all the information that I can. We have reason to believe that a special agent has been despatched from Moscow to this country. We don't know what name he is travelling under, we don't know when he will arrive. But we do know something about him. He is a man who gave us great trouble in the war, a ubiquitous kind of fellow who turned up all over the place where we least wanted him. He is a Russian by birth, and an accomplished linguist-so much so that he can pass as half a dozen other nationalities, including our own. He is also a past master in the art of disguise. And he has brains. It was he who devised the No. 16 code.

"When and how he will turn up, I do not know. But I am fairly certain that he will turn up. We do know this-he was not personally acquainted with the real Mr. Theodore Blunt. I think that he will turn up at your office, on the pretext of a case which he will wish you to take up, and will try you with the passwords. The first, as you know, is the mention of the number sixteen-which is replied to by a sentence containing the same number. The second, which we have only just learnt, is an inquiry as to whether you have ever crossed the Channel. The answer to that is: "I was in Berlin on the 13th of last month." As far as we know, that is all. I would suggest that you reply correctly, and so endeavor to gain his confidence. Sustain the fiction if you possibly can. But even if he appears to be completely deceived, remain on your guard. Our friend is particularly astute, and can play a double game as well, or better, than you can. But in either case, I hope to get him through you. From this day forward I am adopting special precautions. A dictaphone was installed last night in your office, so that one of my men in the room below will be able to hear everything that passes in your office. In this way, I shall be immediately informed if anything arises, and can take the necessary steps to safeguard you and your wife whilst securing the man I am after."

After a few more instructions, and a general discussion of tactics, the two young people departed, and made their way as rapidly as possible to the office of Blunt's Brilliant Detectives.

"It's late," said Tommy, looking at his watch. "Just on twelve o'clock. We've been a long time with the Chief. I hope we haven't missed a particularly spicy case."

"On the whole," said Tuppence, "we've not done badly. I was tabulating results the other day. We've solved four baffling murder mysteries, rounded up a gang of counterfeiters, ditto gang of smugglers-"

"Actually two gangs," interpolated Tommy. "So we have! I'm glad of that. 'Gangs' sounds so professional."

Tuppence continued, ticking off the items on her fingers.

"One jewel robbery, two escapes from violent death, one case of missing lady reducing her figure, one young girl befriended, an alibi successfully exploded, and alas! one case where we made utter fools of ourselves. On the whole, jolly good! We're very clever, I think."

"You would think so," said Tommy. "You always do. Now I have a secret feeling that once or twice we've been rather lucky."

"Nonsense," said Tuppence. "All done by the little grey cells."

"Well, I was damned lucky once," said Tommy. "The day that Albert did his lasso act! But you speak, Tuppence, as though it was all over?"

"So it is," said Tuppence. She lowered her voice impressively. "This is our last case. When they have laid the super spy by the heels, the great detectives intend to retire and take to bee keeping or vegetable-marrow growing. It's always done."

"Tired of it, eh?"

"Ye-es, I think I am. Besides, we're so successful now- the luck might change."

"Who's talking about luck now?" asked Tommy triumphantly.

At that moment they turned in at the doorway of the block of buildings in which the International Detective Bureau had its offices, and Tuppence did not reply.

Albert was on duty in the outer office, employing his leisure in balancing, or endeavoring to balance, the office ruler upon his nose.

With a stern frown of reproof, the great Mr. Blunt passed into his own private office. Divesting himself of his overcoat and hat, he opened the cupboard, on the shelves of which reposed his classic library of the great detectives of fiction.

"The choice narrows," murmured Tommy. "On whom shall I model myself to-day?"

Tuppence's voice, with an unusual note in it, made him turn sharply.

"Tommy," she said. "What day of the month is it?"

"Let me see-the eleventh-why?"

"Look at the calendar."

Hanging on the wall was one of those calendars from which you tear a leaf every day. It bore the legend of Sunday the 16th. To-day was Monday.

"By Jove, that's odd. Albert must have torn off too many. Careless little devil."

"I don't believe he did," said Tuppence. "But we'll ask him."

Albert, summoned and questioned, seemed very astonished. He swore he had only torn off one leaf-that of the day before. His statement was presently supported, for whereas, the leaf torn off by Albert was found in the grate, the succeeding ones were lying in the waste paper basket.

"A neat and methodical criminal," said Tommy. "Who's been here this morning, Albert? A client of any kind?"

"Just one, sir."

"What was he like?"

"It was a she. A Hospital Nurse. Very upset and anxious to see you. Said she'd wait until you came. I put her in 'Clerks' because it was warmer."

"And from there she could walk in here, of course, without your seeing her. How long has she been gone?"

"About half an hour, sir. Said she'd call again this afternoon. A nice motherly looking body."

"A nice motherly-oh! get out, Albert."

Albert withdrew, injured.

"Queer start, that," said Tommy. "It seems a little purposeless. Puts us on our guard. I suppose there isn't a bomb concealed in the fireplace or anything of that kind?"

He reassured himself on that point, then he seated himself at the desk and addressed Tuppence.

"Mon ami," he said. "We are here faced with a matter of the utmost gravity. You recall, do you not, the man who was No. 4. Him whom I crushed like an egg shell in the Dolomites-with the aid of high explosives, bien entendu. But he was not really dead-ah! no, they are never really dead, these super criminals. This is the man-but even more so, if I may so put it. He is the 4 squared-in other words, he is now the No. 16. You comprehend, my friend?"

"Perfectly," said Tuppence. "You are the great Hercule Poirot."

"Exactly. No moustaches, but lots of grey cells."

"I've a feeling," said Tuppence, "that this particular adventure will be called the 'Triumph of Hastings.' "

"Never," said Tommy. "It isn't done. Once the idiot friend, always the idiot friend. There's an etiquette in these matters. By the way, man ami, can you not part your hair in the middle instead of one side? The present effect is unsymmetrical and deplorable."

The buzzer rang sharply on Tommy's desk. He returned the signal and Albert appeared bearing a card.

"Prince Vladiroffsky," read Tommy, in a low voice. He looked at Tuppence. "I wonder-Show him in, Albert."

The man who entered was of middle height, graceful in bearing, with a fair beard, and apparently about thirty-five years of age.

"Mr. Blunt?" he inquired. His English was perfect. "You have been most highly recommended to me. Will you take up a case for me?"

"If you will give me the details-?"

"Certainly. It concerns the daughter of a friend of mine-a girl of sixteen. We are anxious for no scandal-you understand."

"My dear sir," said Tommy. "This business has been running successfully for sixteen years owing to our strict attention to that particular principle."

He fancied he saw a sudden gleam in the other's eye. If so, it passed as quickly as it came.

"You have branches, I believe, on the other side of the Channel?"

"Oh! yes. As a matter of fact," he brought out the word with great deliberation, "I myself was in Berlin on the 13th of last month."

"In that case," said the stranger, "it is hardly necessary to keep up the little fiction. The daughter of my friend can be conveniently dismissed. You know who I am-at any rate I see you have had warning of my coming."

He nodded towards the calendar on the wall.

"Quite so," said Tommy.

"My friends-I have come over here to investigate matters. What has been happening?"

"Treachery," said Tuppence, no longer able to remain quiescent.

The Russian shifted his attention to her, and raised his eyebrows.