Salt had only known Miss Lisle for a few months, and for a third of the period he had not seen her. But he knew that when she showed a disposition to take up his time something more than the amenities of conversation lay behind her words. He remembered that level glance. It foreshadowed another "long pointless tale."

"For instance?" he suggested encouragingly.

"If I left this office locked when I went out to lunch, for instance, and found it still locked but the papers slightly disarranged on my return," she replied.

"Anything more?"

"It is very unpleasant to set traps, of course, but if I put a little dab of typewriter ink on the inner handle of the door when I next went out, and subsequently found a slight stain of a similar colour on my white glove after shaking hands with some one, the suspicion would be deepened."

"I think that the matter is of sufficient importance for you to tell me all you know," he said gravely. "If you hesitate to be definite for fear of making a mistake, I will take pains to verify your suspicions and I will accept all responsibility."

"Then I accuse Mr Tantroy of being a paid spy in the service of the Government."

"Tantroy!" exclaimed Salt with a momentary feeling of incredulity.

"Tantroy! It seems impossible, but, after all, it is possible enough.

You know, of course, that he has a room here now, and might even think in his inexperience that he was at liberty to come into this office at any time."

"But not to take impressions of my keys and have duplicates made; nor to copy extracts in my absence; nor to open and examine the cipher typewriter."

"Has that been left unlocked?" he demanded sharply.

"No," she replied. "You have the only key that I know of. But it _has_ been unlocked, and I infer that the code has been copied."

For quite three minutes there was silence. Salt was thinking, not idly, but estimating exactly the effect of what had happened. Miss Lisle was waiting, with somewhat rare perception, until he was ready to continue.

"Sooner or later something of the sort was bound to come," he summed up quietly, without a trace of discomfiture. "It is only the personality that is surprising. His interests are identical with ours; he has everything to gain by our success. Why; why on earth?"

"I think that I can explain that in three words," suggested Miss Lisle.

"Velma St Saint."

Salt looked enquiringly. He had forgotten the Hon. Freddy's deity for the moment.

"Of the Vivarium," added Irene.

"Oh, the lady who hangs by her toes," he remarked with enlightenment.

"'The World's Greatest Inverted Cantatrice'!" quoted Miss Lisle. "That is her celebrated 'Upside Down' song that the organ is playing in the street below. A few years ago she got a week's engagement at the Elysium at a salary of eighty pounds. She calculated from that that she could afford to spend four thousand a year, and although all theatrical incomes have steadily declined ever since until she only gets ten pounds a week now, she has never been able to make any difference in her style of living.... Of course there is a deficit to be made up."

"It is just as well. If it had not been Tantroy it would have been some one abler. Now what has he done, what has he learned?"

"Duplicate keys of this door and of my desk have been made. The lock of the cipher typewriter case is not of an elaborate pattern, and any one bringing a quant.i.ty of keys of the right size would probably find one to answer. I don't think that either your desk or the safe has been opened; certainly not since I began to notice. The papers to which he would have access are consequently not highly important."

"Letters?" suggested Salt. "For instance, my letters lying here until you forwarded them. There is a post in at eight o'clock in the morning; others after you have left up to ten at night. There would be every opportunity for abstracting some, opening them at leisure, and then dropping them into the letter-box again a little later."

"No," said Miss Lisle. "I took precautions against that."

"How?" he demanded, and waited very keenly for her answer.

"Simply by arriving here before eight and remaining until ten."

"Thank you." It was all he said, but it did not leave Miss Lisle with the empty feeling that virtue had merely been its own reward.

"Perhaps I ought to add that Mr Tantroy tried to get information from me," she remarked distantly. "He--he came here frequently and wished me to accept presents; boxes of chocolate at first, I think, and jewellery afterwards. It was a mistake he made."

"Yes," a.s.sented Salt thoughtfully, "I think it was. There is one other thing, Miss Lisle. You could scarcely know with whom he was negotiating on the other side?"

"No," she admitted regretfully; "I had not sufficient time. That was why I did not wish to go away just now."

"I do not think that you need hesitate to leave it now. I am not taking it out of your hands, only carrying on another phase that you have made possible. It will simplify matters if I have the office to myself. Could you find an opportunity for telling Tantroy casually that you are taking a fortnight's holiday?"

Her answer hung just a moment. Had he known Tantroy better he might have guessed. "Yes, certainly," she replied hastily, with a little stumble in her speech.

Perhaps he guessed. "No," he corrected himself. "On second thoughts, it does not matter."

"I do not mind," she protested loyally.

"If it were necessary I should not hesitate to ask you," he replied half brusquely. "It is not."

"Very well. I will go to-morrow."

That evening, when he was alone. Salt unlocked the typewriter case to which Miss Lisle had alluded, took out the machine, and seating himself before it proceeded to compose a letter upon which he seemed to spend much consideration. As his fingers struck the keys, upon the sheet of paper in the carrier there appeared the following mystifying composition:

kbeljsl

wopmjvsjxkivslilscalkwespljkjscwecsspssp fxfejsloxmjcneoeqjdncs----

It was, in fact, as Miss Lisle had said, a code typewriter. The letters which appeared on the paper did not correspond with the letters on the keys. According to the keyboard the writing should have been:

mydrstr

nwhvsltscmpltrprtbfrmndthrsmstbndbtthtth prpslhvfrmltdsfsblndth----

and signified, to resolve it into its ultimate form:

MY DEAR ESTAIR,--I now have Salt's complete report before me, and there seems to be no doubt that the proposal I have formulated is feasible, and the----

Written without vowels, stops, capitals, or s.p.a.ces, this gave a very serviceable cryptograph, but there was an added safeguard. After completing the first line the writer moved a shift-key and brought another set of symbols into play--or, rather, the same symbols under a different arrangement. The process was repeated for the third line, and then the fourth line returned to the system of the first. Thus three codes were really in operation, and the danger of the key being found by the frequent recurrence of certain symbols (the most fruitful cause of detection) was almost overcome. Six identical machines were in existence. One has been accounted for; Sir John Hampden had another; and a third was in the possession of Robert Estair, the venerable t.i.tular head of the combined Imperial party. A sociable young publican, who had a very snug house in the neighbourhood of Westminster Abbey, could have put his hand upon the fourth; the fifth was in the office of a super-phosphate company carrying on an unostentatious business down a quiet little lane about ten or a dozen miles out of London; and the sixth had fallen to the lot of a busy journalist, who seemed to have the happy knack of getting political articles and paragraphs accepted without demur by all the leading newspapers by the simple expedient of scribbling "Urgent" and some one else's initials across the envelopes he sent them in. Communications of the highest importance never reached the stage of ink and paper, but the six machines were in frequent use. In _bona fide_ communications the customary phraseology with which letters begin and end was not used, it is perhaps unnecessary to say. So obvious a clue as the short line "kbeljsl" at the head of a letter addressed to Estair would be as fatal to the secrecy of any code as the cartouched "Cleopatra" and "Ptolemy" were to the mystery of Egyptian hieroglyphics.

That Salt wrote it may be taken as an indication that he had another end in view; and it is sometimes a mistake to overrate the intelligence of your opponents. When the letter was finished he put it away in his pocket-book, arranged the fastenings of both safe and desk so that he could tell if they had been disturbed, and then went home.

The next morning his preparations advanced another step. He brought with him a new letter copying-book, a silver cigarette-case with a plain polished surface, and a small jar of some oily preparation. With a little of the substance from the jar he smeared the cigarette-case all over, wiped away the greater part again until nothing but an almost imperceptible trace remained, and then placed it carefully within his desk. The next detail was to write a dozen letters with dates extending over the last few days. All were short; all were quite unimportant; they were chiefly concerned with appointments, references to future League meetings, and the like. Some few were written in cipher, but the majority were plain reading, and Salt signed them all in Sir John's name, appending his own initials. To sign the long letter which he had already written he cut off from a note in the baronet's own handwriting the signature "John Hampden," fastened it lightly at the foot of the typewritten sheet, and then proceeded to copy all the letters into the new book. The effect was patent: one letter and one alone stood out among the rest as of pre-eminent importance. The completion was reached by gumming upon the back of the book a label inscribed "Hampden.

Private," treating the leather binding with a coating of the preparation from the jar, and finally subst.i.tuting it in the safe in place of the genuine volume. Then he burned his originals of all the fict.i.tious letters and turned to other matters.

It was not until two days later that Mr Tantroy paid Salt a pa.s.sing visit. He dropped in in a friendly way with the plea that the burden of his own society in his own room, where he apparently spent two hours daily in thinking deeply, had grown intolerable.

"You are always such a jolly busy, energetic chap, Salt, that it quite bucks me up to watch you," he explained.

Salt, however, was not busy that afternoon. He only excused himself to ring for a note, which was lying before him already addressed, to be taken out, and then gave his visitor an undivided attention. He was positively entertaining over his recent journeyings. Freddy Tantroy had never thought that the chap had so much in him before.