plicate 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 in