Dusk found Stuart in a singular frame of mind. He was torn between duty—or what he conceived to be his duty—to the community, and … something else. A messenger from New Scotland Yard had brought him a bundle of documents relating to the case of Sir Frank Narcombe, and a smaller packet touching upon the sudden end of Henrik Ericksen, the Norwegian electrician, and the equally unexpected death of the Grand Duke Ivan. There were medical certificates, proceedings of coroners, reports of detectives, evidence of specialists and statements of friends, relatives and servants of the deceased. A proper examination of all the documents represented many hours of close study.  
Stuart was flattered by the opinion held of his ability by the Assistant Commissioner, but dubious of his chance of detecting any flaw in the evidence which had escaped the scrutiny of so many highly trained observers.
 
He paced the study restlessly. Although more than six hours had elapsed, he had not communicated to Scotland Yard the fact of his having seen Mlle. Dorian that afternoon. A hundred times he had read the message, although he knew it by heart, knew the form of every letter, the odd crossing of the _t'_s and the splashy dotting of the i's.
 
If only he could have taken counsel with someone—with someone not bound to act upon such information—it would have relieved his mental stress. His ideas were so chaotic that he felt himself to be incapable of approaching the task presented by the pile of papers lying upon his table.
 
The night was pleasantly warm and the sky cloudless. Often enough he found himself glancing toward the opened French windows, and once he had peered closely across into the belt of shadow below the hedge, thinking that he had detected something which moved there. Stepping to the window, the slinking shape had emerged into the moonlight—and had proclaimed itself to be that of a black cat!
 
Yet he had been sorely tempted to act upon the advice so strangely offered. He refrained from doing so, however, reflecting that to spend his evenings with closed and barred shutters now that a spell of hot weather seemed to be imminent would be insufferable. Up and down the room he paced tirelessly, always confronted by the eternal problem.
 
Forcing himself at last to begin work if only as a sedative, he filled and lighted his pipe, turned off the centre lamp and lighted the reading lamp upon his table. He sat down to consider the papers bearing upon the death of Eriksen. For half an hour he read on steadily and made a number of pencil notes. Then he desisted and sat staring straight before him.
 
What possible motive could there be in assassinating these people? The case of the Grand Duke might be susceptible of explanation, but those of Henrik Ericksen and Sir Frank Narcombe were not. Furthermore he could perceive no links connecting the three, and no reason why they should have engaged the attention of a common enemy. Such crimes would seem to be purposeless. Assuming that "The Scorpion" was an individual, that individual apparently was a dangerous homicidal maniac.
 
But, throughout the documents, he could discover no clue pointing to the existence of such an entity. "The Scorpion" might be an invention of the fertile brain of M. Gaston Max; for it had become more and more evident, as he had read, that the attempt to trace these deaths to an identical source had originated at the Service de Surete, and it was from Paris that the name "The Scorpion" had come. The fate of Max was significant, of course. The chances of his death proving to have been due to accident were almost negligible and the fact that a fragment of a golden scorpion had actually been found upon his body was certainly curious.
 
"Close your shutters at night…."
 
How the words haunted him and how hotly he despised himself for a growing apprehension which refused to be ignored. It was more mental than physical, this dread which grew with the approach of midnight, and it resembled that which had robbed him of individuality and all but stricken him inert when he had seen upon the moon-bright screen of the curtains the shadow of a cowled man.
 
Dark forces seemed to be stirring, and some unseen menace crept near to him out of the darkness.
 
The house was of early Victorian fashion and massive folding shutters were provided to close the French windows. He never used them, as a matter of fact, but now he tested the fastenings which kept them in place against the inner wall and even moved them in order to learn if they were still serviceable.
 
Of all the mysteries which baffled him, that of the piece of cardboard in the envelope sealed with a Chinese coin was the most irritating. It seemed like the purposeless trick of a child, yet it had led to the presence of the cowled man—and to the presence of Mlle. Dorian. Why?
 
He sat down at his table again.
 
"Damn the whole business!" he said. "It is sending me crazy."
 
Selecting from the heap of documents a large sheet of note-paper bearing a blue diagram of a human bust, marked with figures and marginal notes, he began to read the report to which it was appended—that of Dr. Halesowen. It stated that the late Sir Frank Narcombe had a "horizontal" heart, slightly misplaced and dilatated, with other details which really threw no light whatever upon the cause of his death.
 
"I have a horizontal heart," growled Stuart—"and considering my consumption of tobacco it is certainly dilatated. But I don't expect to drop dead in a theatre nevertheless."
 
He read on, striving to escape from that shadowy apprehension, but as he read he was listening to the night sounds of London, to the whirring of distant motors, the whistling of engines upon the railway and dim hooting of sirens from the Thames. A slight breeze had arisen and it rustled in the feathery foliage of the acacias and made a whispering sound as it stirred the leaves of the privet hedge.
&n............