I was very disappointed with the results of Poirot's bomb attack on the premises in Chinatown. To begin with, the leader of the gang had escaped. When Japp's men rushed up in response to Poirot's whistle they found four Chinamen unconscious in the hall, but the man who had threatened me with death was not among them. I remembered afterwards that when I was forced out on to the doorstep, to decoy Poirot into the house, this man had kept well in the background. Presumably he was out of the danger zone of the gas bomb, and made good his escape by one of the many exits which we afterwards discovered.

From the four who remained in our hands we learnt nothing. The fullest investigation by the police failed to bring to light anything to connect them with the Big Four. They were ordinary low-class residents of the district, and they professed bland ignorance of the name Li Chang Yen. A Chinese gentleman had hired them for service in the house by the waterside, and they knew nothing whatever of his private affairs.

By the next day I had, except for a slight headache, completely recovered from the effects of Poirot's gas bomb. We went down together to Chinatown and searched the house from which I had been rescued. The premises consisted of two ramshackle houses joined together by an underground passage. The ground floors and the upper stories of each were unfurnished and deserted, the broken windows covered by decaying shutters. Japp had already been prying about in the cellars, and had discovered the secret of the entrance to the subterranean chamber where I had spent such an unpleasant half-hour. Closer investigation confirmed the impression that it had made on me the night before. The silks on the walls and divan and the carpets on the floors were of exquisite workmanship. Although I know very little about Chinese art, I could appreciate that every article in the room was perfect of its kind.

With the aid of Japp and some of his men we conducted a most thorough search of the apartment. I had cherished high hopes that we would find documents of importance. A list, perhaps, of some of the more important agents of the Big Four, or cipher notes of some of their plans, but we discovered nothing of the kind. The only papers we found in the whole place were the notes which the Chinaman had consulted whilst he was dictating the letter to Poirot. These consisted of a very complete record of each of our careers, and estimate of our characters, and suggestions about the weaknesses through which we might best be attacked.

Poirot was most childishly delighted with this discovery. Personally I could not see that it was of any value whatever, especially as whoever compiled the notes was ludicrously mistaken in some of his opinions. I pointed this out to my friend when we were back in our rooms.

"My dear Poirot," I said, "you know now what the enemy thinks of us. He appears to have a grossly exaggerated idea of your brain power, and to have absurdly underrated mine, but I do not see how we are better off for knowing this."

Poirot chuckled in rather an offensive way.

"You do not see, Hastings, no? But surely now we can prepare ourselves for some of their methods of attack now that we are warned of some of our faults. For instance my friend, we know that you should think before you act. Again, if you meet a red-haired young woman in trouble you should eye her—what you say—askance, is it not?"

Their notes had contained some absurd references to my supposed impulsiveness, and had suggested that I was susceptible to the charms of young women with hair of a certain shade. I thought Poirot's reference to be in the worst of taste, but fortunately I was able to counter him.

"And what about you?" I demanded. "Are you going to try to cure your 'overweening vanity?' Your 'finicky tidiness?'"

I was quoting, and I could see that he was not pleased with my retort.

"Oh, without doubt, Hastings, in some things they deceive themselves—tant mieux! They will learn in due time. Meanwhile we have learnt something, and to know is to be prepared."

This last was a favourite axiom of his lately; so much so that I had begun to hate the sound of it.

"We know something, Hastings," he continued. "Yes, we know something—and that is to the good—but we do not know nearly enough. We must know more."

"In what way?"

Poirot settled himself back in his chair, straightened a box of matches which I had thrown carelessly down on the table, and assumed an attitude that I knew only too well. I saw that he was prepared to hold forth at some length.

"See you, Hastings, we have to contend against four adversaries; that is, against four different personalities. With Number One we have never come into personal contact—we know him, as it were, only by the impress of his mind—and in passing, Hastings, I will tell you that I begin to understand that mind very well—a mind most subtle and Oriental—every scheme and plot that we have encountered have emanated from the brain of Li Chang Yen. Number Two and Number Three are so powerful, so high up, that they are for the present immune from our attacks. Nevertheless what is their safeguard is, by a perverse chance, our safeguard also. They are so much in the limelight that their movements must be carefully ordered. And so we come to the last member of the gang—we come to the man known as Number Four."

Poirot's voice altered a little, as it always did when speaking of this particular individual.

"Number Two and Number Three are able to succeed, to go on their way unscathed, owing to their notoriety and their assured position. Number Four succeeds for the opposite reason—he succeeds by the way of obscurity. Who is he? Nobody knows. What does he look like? Again nobody knows. How many times have we seen him, you and I? Five times, is it not? And could either of us say truthfully that we could be sure of recognising him again?"

I was forced to shake my head, as I ran back in my mind over those five different people who, incredible as it seemed, were one and the same man. The burly lunatic asylum keeper, the man in the buttoned up overcoat in Paris, James, the footman, the quiet young medical man in the Yellow Jasmine case, and the Russian Professor. In no way did any two of these people resemble each other.

"No," I said hopelessly. "We've nothing to go by whatsoever."

Poirot smiled.

"Do not, I pray of you, give way to such enthusiastic despair. We know one or two things."

"What kind of things?" I asked sceptically.

"We know that he is a man of medium height, and of medium or fair colouring. If he were a tall man of swarthy complexion he could never have passed himself off as the fair stocky doctor. It is child's play, of course, to put on an additional inch or so for the part of James, or the Professor. In the same way he must have a short straight nose. Additions can be built on to a nose by skilful make up, but a large nose cannot be successfully reduced at a moment's notice. Then again, he must be a fairly young man, certainly not over thirty-five. You see, we are getting somewhere. A man between thirty and thirty-five, of medium height and colouring, an adept in the art of make up, and with very few or any teeth of his own."

"What?"

"Surely, Hastings. As the keeper, his teeth were broken and discoloured, in Paris they were even and white, as the doctor they protruded slightly, and as Savaronoff they had unusually long canines. Nothing alters the face so completely as a different set of teeth. You see where all this is leading us?"

"Not exactly," I said cautiously.

"A man carries his profession written in his face, they say."

"He's a criminal," I cried.

"He is an adept in the art of making up."

"It's the same thing."

"Rather a sweeping statement, Hastings, and one which would hardly be appreciated by the theatrical world. Do you not see that the man is, or has been, at one time or another, an actor?"

"An actor?"

"But certainly. He has the whole technique at his fingertips. Now there are two classes of actors, the one who sinks himself in his part, and the one who manages to impress his personality upon it. It is from the latter class that actor managers usually spring. They seize a part and mould it to their own personality. The former class is quite likely to spend its days doing Mr. Lloyd George at different music halls, or impersonating old men with beards in repertory plays. It is among that former class that we must look for our Number Four. He is a supreme artist in the way he sinks himself in each part he plays."

I was growing interested.

"So you fancy you may be able to trace his identity through his connection with the stage?"

"Your reasoning is always brilliant, Hastings."

"It might have been better," I said coldly, "if the idea had come to you sooner. We have wasted a lot of time."

"You are in error, mon ami. No more time has been wasted than was unavoidable. For some months now my agents have been engaged on the task. Joseph Aarons is one of them. You remember him? They have compiled a list for me of men fulfilling the necessary qualifications—young men round about the age of thirty, of more or less nondescript appearance, and with a gift for playing character parts—men, moreover, who have definitely left the stage within the last three years."

"Well?" I said, deeply interested.

"The list was, necessarily, rather a long one. For some time now, we have been engaged on the task of elimination. And finally we have boiled the whole thing down to four names. Here they are, my friend."

He tossed me over a sheet of paper. I read its contents aloud.

"Ernest Luttrell. Son of a North Country parson. Always had a kink of some kind in his moral make-up. Was expelled from his public school. Went on the stage at the age of twenty-three. (There followed a list of parts he had played, with dates and places.) Addicted to drugs. Supposed to have gone to Australia four years ago. Cannot be traced after leaving England. Age 32, height 5 ft. 10-1/2 in., clean-shaven, hair brown, nose straight, complexion fair, eyes gray.

"John St. Maur. Assumed name. Real name not known. Believed to be of cockney extraction. On stage since quite a child. Did music hall impersonations. Not been heard of for three years. Age, about 33, height 5 ft. 10 in., slim build, blue eyes, fair colouring.

"Austen Lee. Assumed name. Real name Austen Foly. Good family. Always had taste for acting and distinguished himself in that way at Oxford. Brilliant war record. Acted in—(The usual list followed. It included many Repertory plays.) An enthusiast on criminology. Had bad nervous breakdown as the result of a motor accident three and a half years ago, and has not appeared on the stage since. No clue to his present whereabouts. Age 35, height 5 ft. 9-1/2 in., complexion fair, eyes blue, hair brown.

"Claud Darrell. Supposed to be real name. Some mystery about his origin. Played at music halls, and also in Repertory plays. Seems to have had no intimate friends. Was in China in 1919. Returned by way of America. Played a few parts in New York. Did not appear on the stage one night, and has never been heard of since. New York police say most mysterious disappearance. Age about 33, hair brown, fair complexion, gray eyes. Height 5 ft. 10-1/2 in.

"Most interesting," I said, as I laid down the paper. "And so this is the result of the investigation of months? These four names. Which of them are you inclined to suspect?"

Poirot made an eloquent gesture.

"Mon ami, for the moment it is an open question. I would just point out to you that Claud Darrell has been in China and America—a fact not without significance, perhaps, but we must not allow ourselves to be unduly biased by that point. It may be a mere coincidence."

"And the next step?" I asked eagerly.

"Affairs are already in train. Every day cautiously worded advertisements will appear. Friends and relatives of one or the other will be asked to communicate with my solicitor at his office. Even to-day we might—Aha, the telephone! Probably it is, as usual, the wrong number, and they will regret to have troubled us, but it may be—yes, it may be—that something has arisen."

I crossed the room and picked up the receiver.

"Yes, yes. M. Poirot's rooms. Yes, Captain Hastings speaking. Oh, it's you, Mr. McNeil! (McNeil and Hodgson were Poirot's solicitors.) I'll tell him. Yes, we'll come round at once."

I replaced the receiver and turned to Poirot, my eyes dancing with excitement.

"I say, Poirot, there's a woman there. Friend of Claud Darrell's. Miss Flossie Monro. McNeil wants you to come round."

"At the instant!" cried Poirot, disappearing into his bedroom, and reappearing with a hat.

A taxi soon took us to our destination, and we were ushered into Mr. McNeil's private office. Sitting in the arm-chair facing the solicitor was a somewhat lurid looking lady no longer in her first youth. Her hair was of an impossible yellow, and was prolific in curls over each ear, her eyelids were heavily blackened, and she had by no means forgotten the rouge and the lip salve.

"Ah, here is M. Poirot!" said Mr. McNeil. "M. Poirot, this is Miss—er—-Monro, who has very kindly called to give us some information."

"Ah, but that is most kind!" cried Poirot.

He came forward with great empressement, and shook the lady warmly by the hand.

"Mademoiselle blooms like a flower in this dry-as-dust old office," he added, careless of the feelings of Mr. McNeil.

This outrageous flattery was not without effect. Miss Monro blushed and simpered.

"Oh, go on now, Mr. Poirot!" she exclaimed. "I know what you Frenchmen are like."

"Mademoiselle, we are not mute like Englishmen before beauty. Not that I am a Frenchman—I am a Belgian, you see."

"I've been to Ostend myself," said Miss Monro.

The whole affair, as Poirot would have said, was marching splendidly.

"And so you can tell us something about Mr. Claud Darrell?" continued Poirot.

"I knew Mr. Darrell very well at one time," explained the lady. "And I saw your advertisement, being out of a shop for the moment, and my time being my own, I said to myself: There, they want to know about poor old Claudie—lawyers, too—maybe it's a fortune looking for the rightful heir, I'd better go round at once."

Mr. McNeil rose.

"Well, Monsieur Poirot, shall I leave you for a little conversation with Miss Monro?"

"You are too amiable. But stay—a little idea presents itself to me. The hour of the déjeuner approaches. Mademoiselle will perhaps honour me by coming out to luncheon with me?"

Miss Monro's eyes glistened. It struck me that she was in exceedingly low water, and that the chance of a square meal was not to be despised.

A few minutes later saw us all in a taxi, bound for one of London's most expensive restaurants. Once arrived there, Poirot ordered a most delectable lunch, and then turned to his guest.

"And for wine, mademoiselle? What do you say to champagne?"

Miss Monro said nothing—or everything.

The meal started pleasantly. Poirot replenished the lady's glass with thoughtful assiduity, and gradually slid on to the topic nearest his heart.

"The poor Mr. Darrell. What a pity he is not with us."

"Yes, indeed," sighed Miss Monro. "Poor boy, I do wonder what's become of him."

"It is a long time since you have seen him, yes?"

"Oh, simply ages—not since the war. He was a funny boy, Claudie, very close about things, never told you a word about himself. But, of course, that all fits in if he's a missing heir. Is it a title, Mr. Poirot?"

"Alas, a mere heritage," said Poirot unblushingly. "But you see, it may be a question of identification. That is why it is necessary for us to find some one who knew him very well indeed. You knew him very well, did you not, mademoiselle."

"I don't mind telling you, Mr. Poirot. You're a gentleman. You know how to order a lunch for a lady—which is more than some of these young whippersnappers do nowadays. Downright mean, I call it. As I was saying, you being a Frenchman won't be shocked. Ah, you Frenchmen! Naughty, naughty!" She wagged her finger at him in an excess of archness. "Well, there it was, me and Claudie, two young things—what else could you expect? And I've still a kindly feeling for him. Though, mind you, he didn't treat me well—no, he didn't—he didn't treat me well at all. Not as a lady should be treated. They're all the same when it comes to a question of money."

"No, no, mademoiselle, do not say that," protested Poirot, filling up her glass once more. "Could you now describe this Mr. Darrell to me?"

"He wasn't anything so very much to look at," said Flossie Monro dreamily. "Neither tall nor short, you know, but quite well set up. Spruce looking. Eyes a sort of blue-gray. And more or less fair-haired, I suppose. But oh, what an artist! I never saw any one to touch him in the profession! He'd have made his name before now if it hadn't been for jealousy. Ah, Mr. Poirot, jealousy—you wouldn't believe it, you really wouldn't, what we artists have to suffer through jealousy. Why, I remember once at Manchester—"

We displayed what patience we could in listening to a long complicated story about a pantomime, and the infamous conduct of the principal boy. Then Poirot led her gently back to the subject of Claud Darrell.

"It is very interesting, all this that you are able to tell us, mademoiselle, about Mr. Darrell. Women are such wonderful observers—they see everything, they notice the little detail that escapes the mere man. I have seen a woman identify one man out of a dozen others—and why, do you think? She had observed that he had a trick of stroking his nose when he was agitated. Now would a man ever have thought of noticing a thing like that?"

"Did you ever!" cried Miss Monro. "I suppose we do notice things. I remember Claudie, now I come to think of it, always fiddling with his bread at table. He'd get a little piece between his fingers and then dab it round to pick up crumbs. I've seen him do it a hundred times. Why, I'd know him anywhere by that one trick of his."

"Is not that just what I say? The marvellous observation of a woman. And did you ever speak to him about this little habit of his, mademoiselle?"

"No, I didn't, Mr. Poirot. You know what men are! They don't like you to notice things especially if it should seem you were telling them off about it. I never said a word—but many's the time I smiled to myself. Bless you, he never knew he was doing it even."

Poirot nodded gently. I noticed that his own hand was shaking a little as he stretched it out to his glass.

"Then there is always handwriting as a means of establishing identity," he remarked. "Without doubt you have preserved a letter written by Mr. Darrell?"

Flossie Monro shook her head regretfully.

"He was never one for writing. Never wrote me a line in his life."

"That is a pity," said Poirot.

"I tell you what, though," said Miss Monro suddenly. "I've got a photograph if that would be any good?"

"You have a photograph?"

Poirot almost sprang from his seat with excitement.

"It's quite an old one—eight years old at least."

"?a ne fait rien! No matter how old and faded! Ah, ma foi, but what stupendous luck! You will permit me to inspect that photograph, mademoiselle?"

"Why, of course."

"Perhaps you will even permit me to have a copy made? It would not take long."

"Certainly if you like."

Miss Monro rose.

"Well, I must run away," she declared archly. "Very glad to have met you and your friend, Mr. Poirot."

"And the photograph? When may I have it?"

"I'll look it out to-night. I think I know where to lay my hand upon it. And I'll send it to you right away."

"A thousand thanks, mademoiselle. You are all that is of the most amiable. I hope that we shall soon be able to arrange another little lunch together."

"As soon as you like," said Miss Monro. "I'm willing."

"Let me see, I do not think that I have your address?"

With a grand air, Miss Monro drew a card from her hand-bag, and handed it to him. It was a somewhat dirty card, and the original address had been scratched out and another substituted in pencil.

Then, with a good many bows and gesticulations on Poirot's part, we bade farewell to the lady and got away.

"Do you really think this photograph so important?" I asked Poirot.

"Yes, mon ami. The camera does not lie. One can magnify a photograph, seize salient points that otherwise would remain unnoticed. And then there are a thousand details—such as the structure of the ears, which no one could ever describe to you in words. Oh, yes, it is a great chance, this which has come our way! That is why I propose to take precautions."

He went across to the telephone as he finished speaking, and gave a number which I knew to be that of a private detective agency which he sometimes employed. His instructions were clear and definite. Two men were to go to the address he gave, and, in general terms, were to watch over the safety of Miss Monro. They were to follow her wherever she went.

Poirot hung up the receiver and came back to me.

"Do you really think that necessary, Poirot?" I asked.

"It may be. There is no doubt that we are watched, you and I, and since that is so, they will soon know with whom we were lunching to-day. And it is possible that Number Four will scent danger."

About twenty minutes later the telephone bell rang. I answered it. A curt voice spoke into the phone.

"Is that Mr. Poirot? St. James Hospital speaking. A young woman was brought in ten minutes ago. Street accident. Miss Flossie Monro. She is asking very urgently for Mr. Poirot. But he must come at once. She can't possibly last long."

I repeated the words to Poirot. His face went white.

"Quick, Hastings. We must go like the wind."

A taxi took us to the hospital in less than ten minutes. We asked for Miss Monro, and were taken immediately to the accident ward. But a white-capped sister met us in the doorway.

Poirot read the news in her face.

"It is over, eh?"

"She died six minutes ago."

Poirot stood as though stunned.

The nurse, mistaking his emotion, began speaking gently.

"She did not suffer, and she was unconscious towards the last. She was run over by a motor, you know—and the driver of the car did not even stop. Wicked, isn't it? I hope some one took the number."

"The stars fight against us," said Poirot, in a low voice.

"You would like to see her?"

The nurse led the way, and we followed.

Poor Flossie Monro, with her rouge and her dyed hair. She lay there very peacefully, with a little smile on her lips.

"Yes," murmured Poirot. "The stars fight against us—but is it the stars?" He lifted his head as though struck by a sudden idea. "Is it the stars, Hastings? If it is not—if it is not.... Oh, I swear to you, my friend, standing here by this poor woman's body, that I will have no mercy when the time comes!"

"What do you mean?" I asked.

But Poirot had turned to the nurse and was eagerly demanding information. A list of the articles found in her hand-bag was finally obtained. Poirot gave a suppressed cry as he read it over.

"You see, Hastings, you see?"

"See what?"

"There is no mention of a latch-key. But she must have had a latch-key with her. No, she was run down in cold blood, and the first person who bent over her took the key from her bag. But we may yet be in time. He may not have been able to find at once what he sought."

Another taxi took us to the address Flossie Monro had given us, a squalid block of Mansions in an unsavoury neighbourhood. It was some time before we could gain admission to Miss Monro's flat, but we had at least the satisfaction of knowing that no one could leave it whilst we were on guard outside.

Eventually we got in. It was plain that some one had been before us. The contents of drawers and cupboards were strewn all over the floor. Locks had been forced, and small tables had even been overthrown, so violent had been the searcher's haste.

Poirot began to hunt through the débris. Suddenly he stood erect with a cry, holding out something. It was an old fashioned photograph frame—empty.

He turned it slowly over. Affixed to the back was a small round label—a price label.

"It cost four shillings," I commented.

"Mon Dieu! Hastings, use your eyes. That is a new clean label. It was stuck there by the man who took out the photograph, the man who was here before us, but knew that we should come, and so left this for us—Claud Darrell—alias Number Four!"