This sudden and appalling change of weather had sadly affected the mood of the gathering. That part of the carnival planned to take place in the garden was perforce abandoned, together with the firework display. A halfhearted attempt was made at dancing, but the howling of the wind, and the omnipresent dust, perpetually reminded the pleasure-seekers that Khamsîn raged without—raged with a violence unparalleled in the experience of the oldest residents. This was a full-fledged sand-storm, a terror of the Sahara descended upon Cairo.  
But there were few departures, although many of the visitors who had long distances to go, especially those from Mena House, discussed the advisability of leaving before this unique storm should have grown even worse. The general tendency, though, was markedly gregarious; safety seemed to be with the crowd, amid the gaiety, where music and laughter were, rather than in the sand-swept streets.
 
"Guess we've outstayed our welcome!" confided an American lady to Sime. "Egypt wants to drive us all home now."
 
"Possibly," he replied with a smile. "The season has run very late, this year, and so this sort of thing is more or less to be expected."
 
The orchestra struck up a lively one-step, and a few of the more enthusiastic dancers accepted the invitation, but the bulk of the company thronged around the edge of the floor, acting as spectators.
 
Cairn and Sime wedged a way through the heterogeneous crowd to the American Bar.
 
"I prescribe a 'tango,'" said Sime.
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"A 'tango' is—?"
 
"A 'tango,'" explained Sime, "is a new kind of cocktail sacred to this buffet. Try it. It will either kill you or cure you."
 
Cairn smiled rather wanly.
 
"I must confess that I need bucking up a bit," he said: "that confounded sand seems to have got me by the throat."
 
Sime briskly gave his orders to the bar attendant.
 
"You know," pursued Cairn, "I cannot get out of my head the idea that there was someone wearing a crocodile mask in the garden a while ago."
 
"Look here," growled Sime, studying the operations of the cocktail manufacturer, "suppose there were—what about it?"
 
"Well, it's odd that nobody else saw him."
 
"I suppose it hasn't occurred to you that the fellow might have removed his mask?"
 
Cairn shook his head slowly.
 
"I don't think so," he declared; "I haven't seen him anywhere in the hotel."
 
"Seen him?" Sime turned his dull gaze upon the speaker. "How should you know him?"
 
Cairn raised his hand to his forehead in an oddly helpless way.
 
"No, of course not—it's very extraordinary."
 
They took their seats at a small table, and in mutual silence loaded and lighted their pipes. Sime, in common with many young and enthusiastic medical men, had theories—theories of that revolutionary sort which only harsh experience can shatter. Secretly he was disposed to ascribe all the ills to which flesh is heir primarily to a disordered nervous system. It was evident that Cairn's mind persistently ran along a particular groove; something lay back of all this erratic talk; he had clearly invested the Mask of Set with a curious individuality.
 
"I gather that you had a stiff bout of it in London?" Sime said suddenly.
 
Cairn nodded.
 
"Beastly stiff. There is a lot of sound reason in your nervous theory, Sime. It was touch and go with
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me for days, I am told; yet, pathologically, I was a hale man. That would seem to show how nerves can kill. Just a series of shocks—horrors—one piled upon another, did as much for me as influenza, pneumonia, and two or three other ailments together could have done."
 
Sime shook his head wisely; this was in accordance with his ideas.
 
"You know Antony Ferrara?" continued Cairn. "Well, he has done this for me. His damnable practices are worse than any disease. Sime, the man is a pestilence! Although the law cannot touch him, although no jury can convict him—he is a murderer. He controls—forces—"
 
Sime was watching him intently.
 
"It will give you some idea, Sime, of the pitch to which things had come, when I tell you that my father drove to Ferrara's rooms one night, with a loaded revolver in his pocket—"
 
"For"—Sime hesitated—"for protection?"
 
"No." Cairn leant forward across the table—"to shoot him, Sime, shoot him on sight, as one shoots a mad dog!"
 
"Are you serious?"
 
"As God is my witness, if Antony Ferrara had been in his rooms that night, my father would have killed him!"
 
"It would have been a shocking scandal."
 
"It would have been a martyrdom. The man who removes Antony Ferrara from the earth will be doing mankind a service worthy of the highest reward. He is unfit to live. Sometimes I cannot believe that he does live; I expect to wake up and find that he was a figure of a particularly evil dream."
 
"This incident—the call at his rooms—occurred just before your illness?"
 
"The thing which he had attempted that night was the last straw, Sime; it broke me down. From the time that he left Oxford, Antony Ferrara has pursued a deliberate course of crime, of crime so cunning, so unusual, and based upon such amazing and unholy
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knowledge that no breath of suspicion has touched him. Sime, you remember a girl I told you about at Oxford one evening, a girl who came to visit him?"
 
Sime nodded slowly.
 
"Well—he killed her! Oh! there is no doubt about it; I saw her body in the hospital."
 
"How had he killed her, then?"
 
"How? Only he and the God who permits him to exist can answer that, Sime. He killed her without coming anywhere near her—and he killed his adoptive father, Sir Michael Ferrara, by the same unholy means!"
 
Sime watched him, but offered no comment.
 
"It was hushed up, of course; there is no existing law which could be used against him."
 
"Existing law?"
 
"They are ruled out, Sime, the laws that could have reached him; but he would have been burnt at the stake in the Middle Ages!"
 
"I see." Sime drummed his fingers upon the table. "You had those ideas about him at Oxford; and does Dr. Cairn seriously believe the same?"
 
"He does. So would you—you could not doubt it, Sime, not for a moment, if you had seen what we have seen!" His eyes blazed into a sudden fury, suggestive of his old, robust self. "He tried night after night, by means of the same accursed sorcery, which everyone thought buried in the ruins of Thebes, to kill me! He projected—things—"
 
"Suggested these—things, to your mind?"
 
"Something like that. I saw, or thought I saw, and smelt—pah!—I seem to smell them now!—beetles, mummy-beetles, you know, from the skull of a mummy! My rooms were thick with them. It brought me very near to Bedlam, Sime. Oh! it was not merely imaginary. My father and I caught him red-handed." He glanced across at the other. "You read of the death of Lord Lashmore? It was just after you came out."
 
"Yes—heart."
 
"It was his heart, yes—but Ferrara was responsible! That was the business which led my father to drive to Ferrara's rooms with a loaded revolver in his pocket."
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The wind was shaking the windows, and whistling about the building with demoniacal fury as if seeking admission; the band played a popular waltz; and in and out of the open doors came and went groups representative of many ages and many nationalities.
 
"Ferrara," began Sime slowly, "was always a detestable man, with his sleek black hair, and ivory face. Those long eyes of his had an expression which always tempted me to hit him. Sir Michael, if what you say is true—and after all, Cairn, it only goes to show how little we know of the nervous system—literally took a viper to his bosom."
 
"He did. Antony Ferrara was his adopted son, of course; God knows to what evil brood he really belongs."
 
Both were silent for a while. Then:
 
"Gracious heavens!"
 
Cairn started to his feet so wildly as almost to upset the table.
 
"Look, Sime! look!" he cried.
 
Sime was not the only man in the bar to hear, and to heed his words. Sime, looking in the direction indicated by Cairn's extended finger, received a vague impression that a grotesque, long-headed figure had appeared momentarily in the doorway opening upon the room where the dancers were; then it was gone again, if it had ever been there, and he was supporting Cairn, who swayed dizzily, and had become ghastly pale. Sime imagined that the heated air had grown suddenly even more heated. Curious eyes were turned upon, his companion, who now sank back into his chair, muttering:
 
"The Mask, the Mask!"
 
"I think I saw the chap who seems to worry you so much," said Sime soothingly. "Wait here; I will tell the waiter to bring you a dose of brandy; and whatever you do, don't get excited."
 
He made for the door, pausing and giving an order to a waiter on his way, and pushed into the crowd outside. It was long past midnight, and the gaiety, which had been resumed, seemed of a forced and feverish
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sort. Some of the visitors were leaving, and a breath of hot wind swept in from the open doors.
 
A pretty girl wearing a yashmak, who, with two similarly attired companions, was making her way to the entrance, attracted his attention; she seemed to be on the point of swooning. He recognised the trio for the same that had pelted Cairn and himself with confetti earlier in the evening.
 
"The sudden heat has affected your friend," he said, stepping up to them. "My name is Dr. Sime; may I offer you my assistance?"
 
The offer was accepted, and with the three he passed out on to the terrace, where the dust grated beneath the tread, and helped the fainting girl into an arabîyeh. The night was thunderously black, the heat almost insufferable, and the tall palms in front of the hotel bowed before the might of the scorching wind.
 
As the vehicle drove off, Sime stood for a moment looking after it. His face was very grave, for there was a look in the bright eyes of the girl in the ya............