After our adventure in the villa at Passy we returned post haste to London. Several letters were awaiting Poirot. He read one of them with a curious smile, and then handed it to me.

"Read this, mon ami."

I turned first to the signature, "Abe Ryland," and recalled Poirot's words: "the richest man in the world." Mr. Ryland's letter was curt and incisive. He expressed himself as profoundly dissatisfied with the reasons Poirot had given for withdrawing from the South American proposition at the last moment.

"This gives one furiously to think, does it not?" said Poirot.

"I suppose it's only natural he should be a bit ratty."

"No, no, you comprehend not. Remember the words of Mayerling, the man who took refuge here—only to die by the hands of his enemies. 'Number Two is represented by an S with two lines through it—the sign for a dollar, also by two stripes and a star. It may be conjectured therefore that he is an American subject, and that he represents the power of wealth.' Add to those words the fact that Ryland offered me a huge sum to tempt me out of England—and—and what about it, Hastings?"

"You mean," I said, staring, "that you suspect Abe Ryland, the multi-millionaire, of being Number Two of the Big Four."

"Your bright intellect has grasped the idea, Hastings. Yes, I do. The tone in which you said multi-millionaire was eloquent—but let me impress upon you one fact—this thing is being run by men at the top—and Mr. Ryland has the reputation of being no beauty in his business dealings. An able, unscrupulous man, a man who has all the wealth that he needs, and is out for unlimited power."

There was undoubtedly something to be said for Poirot's view. I asked him when he had made up his mind definitely upon the point.

"That is just it. I am not sure. I cannot be sure. Mon ami, I would give anything to know. Let me but place Number Two definitely as Abe Ryland, and we draw nearer to our goal."

"He has just arrived in London, I see by this," I said, tapping the letter. "Shall you call upon him, and make your apologies in person?"

"I might do so."

Two days later, Poirot returned to our rooms in a state of boundless excitement. He grasped me by both hands in his most impulsive manner.

"My friend, an occasion stupendous, unprecedented, never to be repeated, has presented itself! But there is danger, grave danger. I should not even ask you to attempt it."

If Poirot was trying to frighten me, he was going the wrong way to work, and so I told him. Becoming less incoherent, he unfolded his plan.

It seemed that Ryland was looking for an English secretary, one with a good social manner and presence. It was Poirot's suggestion that I should apply for the post.

"I would do it, myself, mon ami," he explained apologetically. "But, see you, it is almost impossible for me to disguise myself in the needful manner. I speak the English very well—except when I am excited—but hardly so as to deceive the ear; and even though I were to sacrifice my moustaches, I doubt not but that I should still be recognisable as Hercule Poirot."

I doubted it also, and declared myself ready and willing to take up the part and penetrate into Ryland's household.

"Ten to one he won't engage me anyway," I remarked.

"Oh, yes, he will. I will arrange for you such testimonials as shall make him lick his lips. The Home Secretary himself shall recommend you."

This seemed to be carrying things a bit far, but Poirot waved aside my remonstrances.

"Oh, yes, he will do it. I investigated for him a little matter which might have caused a grave scandal. All was solved with discretion and delicacy, and now, as you would say, he perches upon my hand like the little bird and pecks the crumbs."

Our first step was to engage the services of an artist in "make up." He was a little man, with a quaint bird-like turn of the head, not unlike Poirot's own. He considered me some time in silence, and then fell to work. When I looked at myself in the glass half an hour afterwards, I was amazed. Special shoes caused me to stand at least two inches taller, and the coat I wore was arranged so as to give me a long, lank, weedy look. My eyebrows had been cunningly altered, giving a totally different expression to my face, I wore pads in my cheeks, and the deep tan of my face was a thing of the past. My moustache had gone, and a gold tooth was prominent on one side of my mouth.

"Your name," said Poirot, "is Arthur Neville. God guard you, my friend—for I fear that you go into perilous places."

It was with a beating heart that I presented myself at the Savoy, at an hour named by Mr. Ryland, and asked to see the great man.

After being kept waiting a minute or two, I was shown upstairs to his suite.

Ryland was sitting at a table. Spread out in front of him was a letter which I could see out of the tail of my eye was in the Home Secretary's handwriting. It was my first sight of the American millionaire, and, in spite of myself, I was impressed. He was tall and lean, with a jutting out chin and slightly hooked nose. His eyes glittered cold and gray behind penthouse brows. He had thick grizzled hair, and a long black cigar (without which, I learned later, he was never seen) protruded rakishly from the corner of his mouth.

"Siddown," he grunted.

I sat. He tapped the letter in front of him.

"According to this piece here, you're the goods all right, and I don't need to look further. Say, are you well up in the social matters?"

I said that I thought I could satisfy him in that respect.

"I mean to say, if I have a lot of dooks and earls and viscounts and suchlike down to the country place I've gotten, you'll be able to sort them out all right and put them where they should be round the dining table?"

"Oh! quite easily," I replied, smiling.

We exchanged a few more preliminaries, and then I found myself engaged. What Mr. Ryland wanted was a secretary conversant with English society, as he already had an American secretary and a stenographer with him.

Two days later I went down to Hatton Chase, the seat of the Duke of Loamshire, which the American millionaire had rented for a period of six months.

My duties gave me no difficulty whatever. At one period of my life I had been private secretary to a busy member of Parliament, so I was not called upon to assume a role unfamiliar to me. Mr. Ryland usually entertained a large party over the week-end, but the middle of the week was comparatively quiet. I saw very little of Mr. Appleby, the American secretary, but he seemed a pleasant, normal young American, very efficient in his work. Of Miss Martin, the stenographer, I saw rather more. She was a pretty girl of about twenty-three or four, with auburn hair and brown eyes that could look mischievous enough upon occasion, though they were usually cast demurely down. I had an idea that she both disliked and distrusted her employer, though, of course, she was careful never to hint at anything of the kind, but the time came when I was unexpectedly taken into her confidence.

I had, of course, carefully scrutinised all the members of the household. One or two of the servants had been newly engaged, one of the footmen, I think, and some of the housemaids. The butler, the housekeeper, and the chef were the duke's own staff, who had consented to remain on in the establishment. The housemaids I dismissed as unimportant; I scrutinised James, the second footman, very carefully; but it was clear that he was an under-footman and an under-footman only. He had, indeed, been engaged by the butler. A person of whom I was far more suspicious was Deaves, Ryland's valet, whom he had brought over from New York with him. An Englishman by birth, with an irreproachable manner, I yet harboured vague suspicions about him.

I had been at Hatton Chase three weeks, and not an incident of any kind had arisen which I could lay my finger on in support of our theory. There was no trace of the activities of the Big Four. Mr. Ryland was a man of overpowering force and personality, but I was coming to believe that Poirot had made a mistake when he associated him with that dread organisation. I even heard him mention Poirot in a casual way at dinner one night.

"Wonderful little man, they say. But he's a quitter. How do I know? I put him on a deal, and he turned me down the last minute. I'm not taking any more of your Monsieur Hercule Poirot."

It was at moments such as these that I felt my cheek pads most wearisome!

And then Miss Martin told me a rather curious story. Ryland had gone to London for the day, taking Appleby with him. Miss Martin and I were strolling together in the garden after tea. I liked the girl very much, she was so unaffected and so natural. I could see that there was something on her mind, and at last out it came.

"Do you know, Major Neville," she said, "I am really thinking of resigning my post here."

I looked somewhat astonished, and she went on hurriedly.

"Oh! I know it's a wonderful job to have got, in a way. I suppose most people would think me a fool to throw it up. But I can't stand abuse, Major Neville. To be sworn at like a trooper is more than I can bear. No gentleman would do such a thing."

"Has Ryland been swearing at you?"

She nodded.

"Of course, he's always rather irritable and short tempered. That one expects. It's all in the day's work. But to fly into such an absolute fury—over nothing at all. He really looked as though he could have murdered me! And, as I say, over nothing at all!"

"Tell me about it?" I said, keenly interested.

"As you know, I open all Mr. Ryland's letters. Some I hand on to Mr. Appleby, others I deal with myself, but I do all the preliminary sorting. Now there are certain letters that come, written on blue paper, and with a tiny 4 marked on the corner—I beg your pardon, did you speak?"

I had been unable to repress a stifled exclamation, but I hurriedly shook my head, and begged her to continue.

"Well, as I was saying, these letters come, and there are strict orders that they are never to be opened, but to be handed over to Mr. Ryland intact. And, of course, I always do so. But there was an unusually heavy mail yesterday morning, and I was opening the letters in a terrific hurry. By mistake I opened one of these letters. As soon as I saw what I had done, I took it to Mr. Ryland and explained. To my utter amazement he flew into the most awful rage. As I tell you, I was quite frightened."

"What was there in the letter, I wonder, to upset him so?"

"Absolutely nothing—that's just the curious part of it. I had read it before I discovered my mistake. It was quite short. I can still remember it word for word, and there was nothing in it that could possibly upset any one."

"You can repeat it, you say?" I encouraged her.

"Yes." She paused a minute and then repeated slowly, whilst I noted down the words unobtrusively, the following:—

"Dear Sir,—The essential thing now, I should say, is to see the property. If you insist on the quarry being included, then seventeen thousand seems reasonable. 11% commission too much, 4% is ample.

"Yours truly,

"Arthur Leversham."

Miss Martin went on:—

"Evidently about some property Mr. Ryland was thinking of buying. But really, I do feel that a man who can get into a rage over such a trifle is, well, dangerous. What do you think I ought to do, Major Neville? You've more experience of the world than I have."

I soothed the girl down, pointed out to her that Mr. Ryland had probably been suffering from the enemy of his race—dyspepsia. In the end I sent her away quite comforted. But I was not so easily satisfied myself. When the girl had gone, and I was alone, I took out my notebook, and ran over the letter which I had jotted down. What did it mean—this apparently innocent-sounding missive? Did it concern some business deal which Ryland was undertaking, and was he anxious that no details about it should leak out until it was carried through? That was a possible explanation. But I remembered the small figure 4 with which the envelopes were marked, and I felt that, at last, I was on the track of the thing we were seeking.

I puzzled over the letter all that evening, and most of the next day—and then suddenly the solution came to me. It was so simple, too. The figure 4 was the clue. Read every fourth word in the letter, and an entirely different message appeared. "Essential should see you quarry seventeen eleven four."

The solution of the figures was easy. Seventeen stood for the seventeenth of October—which was to-morrow, eleven was the time, and four was the signature—either referring to the mysterious Number Four himself—or else it was the "trade-mark" so to speak, of the Big Four. The quarry was also intelligible. There was a big disused quarry on the estate about half a mile from the house—a lonely spot, ideal for a secret meeting.

For a moment or two I was tempted to run the show myself. It would be such a feather in my cap, for once, to have the pleasure of crowing over Poirot.

But in the end I overcame the temptation. This was a big business—I had no right to play a lone hand, and perhaps jeopardise our chances of success. For the first time, we had stolen a march upon our enemies. We must make good this time—and, disguise the fact as I might, Poirot had the better brain of the two.

I wrote off post haste to him, laying the facts before him, and explaining how urgent it was that we should overhear what went on at the interview. If he liked to leave it to me, well and good, but I gave him detailed instructions how to reach the quarry from the station in case he should deem it wise to be present himself.

I took the letter down to the village and posted it myself. I had been able to communicate with Poirot throughout my stay, by the simple expedient of posting my letters myself, but we had agreed that he should not attempt to communicate with me in case my letters should be tampered with.

I was in a glow of excitement the following evening. No guests were staying in the house, and I was busy with Mr. Ryland in his study all the evening. I had foreseen that this would be the case, which was why I had had no hope of being able to meet Poirot at the station. I was, however, confident that I would be dismissed well before eleven o'clock.

Sure enough, just after ten-thirty, Mr. Ryland glanced at the clock, and announced that he was "through." I took the hint and retired discreetly. I went upstairs as though going to bed, but slipped quietly down a side staircase and let myself out into the garden, having taken the precaution to don a dark overcoat to hide my white shirt-front.

I had gone some way down the garden when I chanced to look over my shoulder. Mr. Ryland was just stepping out from his study window into the garden. He was starting to keep the appointment. I redoubled my pace, so as to get a clear start. I arrived at the quarry somewhat out of breath. There seemed no one about, and I crawled into a thick tangle of bushes and awaited developments.

Ten minutes later, just on the stroke of eleven, Ryland stalked up, his hat over his eyes and the inevitable cigar in his mouth. He gave a quick look round, and then plunged into the hollows of the quarry below. Presently I heard a low murmur of voices come up to me. Evidently the other man—or men—whoever they were, had arrived first at the rendezvous. I crawled cautiously out of the bushes, and inch by inch, using the utmost precaution against noise, I wormed myself down the steep path. Only a boulder now separated me from the talking men. Secure in the blackness, I peeped round the edge of it and found myself facing the muzzle of a black, murderous-looking automatic!

"Hands up!" said Mr. Ryland succinctly. "I've been waiting for you."

He was seated in the shadow of the rock, so that I could not see his face, but the menace in his voice was unpleasant. Then I felt a ring of cold steel on the back of my neck, and Ryland lowered his own automatic.

"That's right, George," he drawled. "March him around here."

Raging inwardly, I was conducted to a spot in the shadows, where the unseen George (whom I suspected of being the impeccable Deaves), gagged and bound me securely.

Ryland spoke again in a tone which I had difficulty in recognising, so cold and menacing was it.

"This is going to be the end of you two. You've got in the way of the Big Four once too often. Ever heard of land slides? There was one about here two years ago. There's going to be another to-night. I've fixed that good and square. Say, that friend of yours doesn't keep his dates very punctually."

A wave of horror swept over me. Poirot! In another minute he would walk straight into the trap. And I was powerless to warn him. I could only pray that he had elected to leave the matter in my hands, and had remained in London. Surely, if he had been coming, he would have been here by now.

With every minute that passed, my hopes rose.

Suddenly they were dashed to pieces. I heard footsteps—cautious footsteps, but footsteps nevertheless. I writhed in impotent agony. They came down the path, paused, and then Poirot himself appeared, his head a little on one side, peering into the shadows.

I heard the growl of satisfaction Ryland gave as he raised the big automatic and shouted "Hands up." Deaves sprang forward as he did so, and took Poirot in the rear. The ambush was complete.

"Please to meet you, Mr. Hercule Poirot," said the American grimly.

Poirot's self-possession was marvellous. He did not turn a hair. But I saw his eyes searching in the shadows.

"My friend? He is here?"

"Yes, you are both in the trap—the trap of the Big Four."

He laughed.

"A trap?" queried Poirot.

"Say, haven't you tumbled to it yet?"

"I comprehend that there is a trap—yes," said Poirot gently. "But you are in error, monsieur. It is you who are in it—not I and my friend."

"What?" Ryland raised the big automatic, but I saw his gaze falter.

"If you fire, you commit murder watched by ten pairs of eyes, and you will be hanged for it. This place is surrounded—has been for the last hour—by Scotland Yard men. It is checkmate, Mr. Abe Ryland."

He uttered a curious whistle, and as though by magic, the place was alive with men. They seized Ryland and the valet and disarmed them. After speaking a few words to the officer in charge, Poirot took me by the arm, and led me away.

Once clear of the quarry he embraced me with vigour.

"You are alive—you are unhurt. It is magnificent. Often have I blamed myself for letting you go."

"I'm perfectly all right," I said, disengaging myself. "But I'm just a bit fogged. You tumbled to their little scheme, did you?"

"But I was waiting for it! For what else did I permit you to go there? Your false name, your disguise, not for a moment was it intended to deceive!"

"What?" I cried. "You never told me."

"As I have frequently told you, Hastings, you have a nature so beautiful and so honest that unless you are yourself deceived, it is impossible for you to deceive others. Good, then, you are spotted from the first, and they do what I had counted on their doing—a mathematical certainty to any one who uses his gray cells properly—use you as a decoy. They set the girl on—By the way, mon ami, as an interesting fact psychologically, has she got red hair?"

"If you mean Miss Martin," I said coldly. "Her hair is a delicate shade of auburn, but—"

"They are épatant—these people! They have even studied your psychology. Oh! yes, my friend, Miss Martin was in the plot—very much so. She repeats the letter to you, together with her tale of Mr. Ryland's wrath, you write it down, you puzzle your brains—the cipher is nicely arranged, difficult, but not too difficult—you solve it, and you send for me."

"But what they do not know is that I am waiting for just this very thing to happen. I go post haste to Japp and arrange things. And so, as you see, all is triumph!"

I was not particularly pleased with Poirot, and I told him so. We went back to London on a milk train in the early hours of the morning, and a most uncomfortable journey it was.

I was just out of my bath and indulging in pleasurable thoughts of breakfast when I heard Japp's voice in the sitting-room. I threw on a bathrobe and hurried in.

"A pretty mare's nest you've got us into this time," Japp was saying. "It's too bad of you, M. Poirot. First time I've ever known you take a toss."

Poirot's face was a study. Japp went on.

"There were we, taking all this Black Hand stuff seriously—and all the time it was the footman."

"The footman?" I gasped.

"Yes, James, or whatever his name is. Seems he laid 'em a wager in the servants' hall that he could get taken for the old man by his nibs—that's you, Captain Hastings—and would hand him out a lot of spy stuff about a Big Four gang."

"Impossible!" I cried.

"Don't you believe it. I marched our gentleman straight to Hatton Chase, and there was the real Ryland in bed and asleep, and the butler and the cook and God knows how many of them to swear to the wager. Just a silly hoax—that's all it was—and the valet is with him."

"So that was why he kept in the shadow," murmured Poirot.

After Japp had gone we looked at each other.

"We know, Hastings," said Poirot at last. "Number Two of the Big Four is Abe Ryland. The masquerading on the part of the footman was to ensure a way of retreat in case of emergencies. And the footman—"

"Yes," I breathed.

"Number Four," said Poirot gravely.