The telephone bell rang.  
Stuart reached across for the instrument and raised the receiver. "Yes," he said—"Dr. Stuart speaking. Inspector Dunbar is here. Hold on."
 
He passed the instrument to Dunbar, who had stood up on hearing his name mentioned. "Sergeant Sowerby at Scotland Yard wishes to speak to you, Inspector."
 
"Hullo," said Dunbar—"that you, Sowerby. Yes—but I arrived here only a short time ago. What's that?—Max? Good God! what does it all mean! Are you sure of the number—49685? Poor chap—he should have worked with us instead of going off alone like that. But he was always given to that sort of thing. Wait for me. I'll be with you in a few minutes. I can get a taxi. And, Sowerby—listen! It's 'The Scorpion' case right enough. That bit of gold found on the dead man is not a cactus stem; it's a scorpion's tail!"
 
He put down the telephone and turned to Stuart, who had been listening to the words with growing concern. Dunbar struck his open palm down on to the table with a violent gesture.
 
"We have been asleep!" he exclaimed. "Gaston Max of the Paris Service has been at work in London for a month, and we didn't know it!"
 
"Gaston Max!" cried Start—"then it must be a big case indeed."
 
As a student of criminology the name of the celebrated Frenchman was familiar to him as that of the foremost criminal investigator in Europe, and he found himself staring at the fragment of gold with a new and keener interest.
 
"Poor chap," continued Dunbar—"it was his last. The body brought in from Hanover Hole has been identified as his."
 
"What! it is the body of Gaston Max!"
 
"Paris has just wired that Max's reports ceased over a week ago. He was working on the case of Sir Frank Narcombe, it seems, and I never knew! But I predicted a long time ago that Max would play the lone-hand game once too often. They sent particulars. The identification disk is his. Oh! there's no doubt about it, unfortunately. The dead man's face is unrecognizable, but it's not likely there are two disks of that sort bearing the initials G.M. and the number 49685. I'm going along now. Should you care to come, doctor?"
 
"I am expecting a patient, Inspector," replied Stuart—"er—a special case. But I hope you will keep me in touch with this affair?"
 
"Well, I shouldn't have suggested your coming to the Yard if I hadn't wanted to do that. As a matter of fact, this scorpion job seems to resolve itself into a case of elaborate assassination by means of some unknown poison; and although I should have come to see you in any event, because you have helped me more than once, I came to-night at the suggestion of the Commissioner. He instructed me to retain your services if they were available."
 
"I am honoured," replied Stuart. "But after all, Inspector, I am merely an ordinary suburban practitioner. My reputation has yet to be made. What's the matter with Halesowen of Upper Wimpole Street? He's the big man."
 
"And if Sir Frank Narcombe was really poisoned—as Paris seems to think he was—he's also a big fool." retorted Dunbar bluntly. "He agreed that death was due to heart trouble."
 
"I know he did; unsuspected ulcerative endocarditis. Perhaps he was right."
 
"If he was right," said Dunbar, taking up the piece of gold from the table, "what was Gaston Max doing with this thing in his possession?"
 
"There may be no earthly connection between Max's inquiries and the death of Sir Frank."
 
"On the other hand—there may! Leaving Dr. Halesowen out of the question, are you open to act as expert adviser in this case?"
 
"Certainly; delighted."
 
"Your fee is your own affair, doctor. I will communicate with you later, if you wish, or call again in the morning."
 
Dunbar wrapped up the scorpion's tail in the piece of tissue paper and was about to replace it in his note-case. Then:
 
"I'll leave this with you, doctor," he said. "I know it will be safe enough, and you might like to examine it at greater leisure."
 
"Very well," replied Stuart. "Some of the engraving is very minute.
I will have a look at it through a glass later."
 
He took the fragment from Dunbar, who had again unwrapped it, and, opening a drawer of the writing-table in which he kept his cheque-book and some few other personal valuables, he placed the curious piece of gold-work within and relocked the drawer.
 
"I will walk as far as the cab-rank with you," he said, finding himself to be possessed of a spirit of unrest. Whereupon the two went out of the room, Stuart extinguishing the lamps as he came to the door.
 
They had not left the study for more than two minutes ere a car drew up outside the house, and Mrs. M'Gregor ushered a lady into the room but lately quitted by Stuart and Dunbar, turning up the lights as she entered.
 
"The doctor has gone out but just now, Miss Dorian," she said stiffly. "I am sorry that ye are so unfortunate in your veesits. But I know he'll be no more than a few minutes."
 
The girl addressed was of a type fully to account for the misgivings of the shrewd old Scotswoman. She had the slim beauty of the East allied to the elegance of the West. Her features, whilst cast in a charming European mould, at the same time suggested in some subtle way the Oriental. She had the long, almond-shaped eyes of the Egyptian, and her hair, which she wore unconventionally in a picturesque fashion reminiscent of the harem, was inclined to be "fuzzy," but gleamed with coppery tints where the light touched its waves.
 
She wore a cloak of purple velvet having a hooded collar of white fox fur; it fastened with golden cords. Beneath it was a white and gold robe, cut with classic simplicity of line and confined at the waist by an ornate Eastern girdle. White stockings and dull gold shoes exhibited to advantage her charming little feet and slim ankles, and she carried a handbag of Indian beadwork. Mlle. Dorian was a figure calculated to fire the imagination of any man and to linger long and sweetly in the memory.
 
Mrs. M'Gregor, palpably ill at ease, conducted her to an armchair.
 
"You are very good," said the visitor, speaking with a certain hesitancy and with a slight accent most musical and fascinating. "I wait a while if I may."
 
"Dear, dear," muttered Mrs. M'Gregor, beginning to poke the fire, "he has let the fire down, of course! Is it out? No … I see a wee sparkie!"
 
She set the poker upright before the nearly extinguished fire and turned triumphantly to Mlle. Dorian, who was watching her with a slight smile.
 
"That will be a comforting blaze in a few minutes, Miss Dorian," she said, and went towards the door.
 
"If you please," called the girl, detaining her—"do you permit me to speak on the telephone a moment? As Dr. Stuart is not at home, I must explain that I wait for him."
 
"Certainly, Miss Dorian," replied Mrs. M'Gregor; "use the telephone by all means. But I think the doctor will be back any moment now."
 
"Thank you so much."
 
Mrs. M'Gregor went out, not without a final backward glance at the elegant figure in the armchair. Mlle. Dorian was seated, her chin resting in her hand and her elbow upon the arm of the chair, gazing into the smoke arising from the nearly extinguished ember of the fire. The door closed, and Mrs. M'Gregor's footsteps could be heard receding along the corridor.
 
Mlle. Dorian sprang from the chair and took out of her handbag a number of small keys attached to a ring. Furtively she crossed the room, all the time listening intently, and cast her cloak over the back of the chair which was placed before the writing-table. Her robe of white and gold clung to her shapely figure as she bent over the table and tried three of the keys in the lock of the drawer which contained Stuart's cheque-book and in which he had recently placed the mysterious gold ornament. The third key fitted the lock, and Mlle. Dorian pulled open the drawer. She discovered first the cheque-book and next a private account-book; then from under the latter she drew out a foolscap envelope sealed with red wax and bearing, in Stuart's handwriting, the address:
 
  Lost Property Office,
  Metropolitan Police,
  New Scotland Yard, S. W. I.
 
She uttered a subdued exclamation; then, as a spark of light gleamed within the open drawer, she gazed as if stupefied at the little ornament which she had suddenly perceived lying near the cheque-book. She picked it up and stared at it aghast. A moment she hesitated; then, laying down the fragment of gold and also the long envelope upon the table, she took up the telephone. Keeping her eyes fixed upon the closed door of the study, she asked for the number East 89512, and whilst she waited for the connection continued that nervous watching and listening. Suddenly she began to speak, in a low voice.
 
"Yes! … Miska speaks. Listen! One of the new keys—it fits. I have the envelope. But, also in the same drawer, I find a part of a broken gold 'agrab (scorpion). Yes, it is broken. It must be they find it, on him." Her manner grew more and more agitated. "Shall I bring it? The envelope it is very large. I do not know if——"
 
From somewhere outside the house came a low, wailing cry—a cry which Stuart, if he had heard it, must have recognized to be identical with that which he had heard in the night—but which he had forgotten to record in his written account.
 
"Ah!" whispered the girl—"there is the signal! It is the doctor who returns." She listened eagerly, fearfully, to the voice which spoke over the wires. "Yes—yes!"
 
Always glancing toward the door, she put down the instrument, took up the long envelope and paused for a moment, thinking that she had heard the sound of approaching footsteps. She exhibited signs of nervous indecision, tried to thrust the envelope into her little bag and realized that even folded it would not fit so as to escape observation. She ran across to the grate and dropped the envelope upon the smouldering fire. As she did so, the nicely balanced poker fell with a clatter upon the tiled hearth.
 
She started wildly, ran back to the table, took up the broken ornament and was about to thrust it into the open drawer, when the study door was flung open and Stuart came in.