inspector dunbar stood in the little dispensary tapping his teeth with the end of a fountain-pen.

"the last time he visited you, doctor—the time when he gave you the envelope—did the cabman wait here in the waiting-room?"

"he did—yes. he came after my ordinary consulting hours and i was at supper, i remember, as i am compelled to dine early."

"he would be in here alone?"

"yes. no one else was in the room."

"would he have had time to find the box, cut out the piece of cardboard from the lid, put it in the envelope and seal it?"

"ample time. but what could be his object? and why mark the envelope 30?"

"it was in your consulting-room that he asked you to take charge of the envelope?"

"yes."

"might i take a peep at the consulting room?"

"certainly, inspector."

from the waiting-room they went up a short flight of stairs into the small apartment in which stuart saw his patients. dunbar looked slowly about him, standing in the middle of the room, then crossed and stared out of the window into the narrow lane below.

"where were you when he gave you the envelope?" he snapped suddenly.

"at the table," replied stuart with surprise.

"was the table-lamp alight?"

"yes. i always light it when seeing patients."

"did you take the letter into the study to seal it in the other envelope?"

"i did, and he came along and witnessed me do it."

"ah," said dunbar, and scribbled busily in his note-book. "we are badly tied at scotland yard, doctor, and this case looks like being another for which somebody else will reap the credit. i am going to make a request that will surprise you."

he tore a leaf out of the book and folded it carefully.

"i am going to ask you to seal up something and lock it away! but i don't think you'll be troubled by cowled burglars or beautiful women because of it. on this piece of paper i have written—a"—he ticked off the points on his fingers: "what i believe to be the name of the man who cut out the cardboard and sealed it in an envelope; b: the name of the cabman; and, c: the name of the man who rang me up here last night and gave me information which had only just reached the commissioner. i'll ask you to lock it away until it's wanted, doctor."

"certainly, if you wish it," replied stuart. "come into the study and you shall see me do as you direct. i may add that the object to be served is not apparent to me."

entering the study, he took an envelope, enclosed the piece of paper, sealed the lapel and locked the envelope in the same drawer of the bureau which once had contained that marked 30.

"mlle. dorian has a duplicate key to this drawer." he said. "are you prepared to take the chance?"

"quite," replied dunbar, smiling; "although my information is worth more than that which she risked so much to steal."

"it's most astounding. at every step the darkness increases. why should anyone have asked me to lock up a blank piece of cardboard?"

"why, indeed," murmured dunbar. "well, i may as well get back. i am expecting a report from sowerby. look after yourself, sir. i'm inclined to think your pretty patient was talking square when she told you there might be danger."

stuart met the glance of the tawny eyes.

"what d'you mean, inspector? why should i be in danger?"

"because," replied inspector dunbar, "if 'the scorpion' is a poisoner, as the chief seems to think, there's really only one man in england he has to fear, and that man is dr. keppel stuart."

when the inspector had taken his departure stuart stood for a long time staring out of the study window at the little lawn with its bordering of high neatly-trimmed privet above which at intervals arose the mop crowns of dwarf acacias. a spell of warm weather seemed at last to have begun, and clouds of gnats floated over the grass, their minute wings glittering in the sunshine. despite the nearness of teeming streets, this was a backwater of london's stream.

he sighed and returned to some work which the visit of the scotland

yard man had interrupted.

later in the afternoon he had occasion to visit the institution to which he had recently been appointed as medical officer, and in contemplation of the squalor through which his steps led him he sought forgetfulness of the scorpion problem—and of the dark eyes of mlle. dorian. he was not entirely successful, and returning by a different route he lost himself in memories which were sweetly mournful.

a taxicab passed him, moving slowly very close to the pavement. he scarcely noted it until it had proceeded some distance ahead of him. then its slow progress so near to the pavement at last attracted his attention, and he stared vacantly towards the closed vehicle.

mlle. dorian was leaning out of the window and looking back at him!

stuart's heart leapt high. for an instant he paused, then began to walk rapidly after the retreating vehicle. perceiving that she had attracted his attention, the girl extended a white-gloved hand from the window and dropped a note upon the edge of the pavement. immediately she withdrew into the vehicle—which moved away at accelerated speed, swung around the next corner and was gone.

stuart ran forward and picked up the note. without pausing to read it, he pressed on to the corner. the cab was already two hundred yards away, and he recognized pursuit to be out of the question. the streets were almost deserted at the moment, and no one apparently had witnessed the episode. he unfolded the sheet of plain note-paper, faintly perfumed with jasmine, and read the following, written in an uneven feminine hand:

"close your shutters at night. do not think too bad of me."