en
it. He walked on.

Automatically his reflections led him to Mlle. Dorian, and he
remembered that even as he paced along there beside the river the
wonderful mechanism of New Scotland Yard was in motion, its many
tentacles seeking--seeking tirelessly--for the girl, whose dark eyes
haunted his sleeping and waking hours. _He_ was responsible, and if
she were arrested _he_ would be called upon to identify her. He
condemned himself bitterly.

After all, what crime had she committed? She had tried to purloin a
letter--which did not belong to Stuart in the first place. And she had
failed. Now--the police were looking for her. His reflections took a
new form.

What of Gaston Max, foremost criminologist in Europe, who now lay dead
and mutilated in an East-End mortuary? The telephone message which had
summoned Dunbar away had been too opportune to be regarded as a mere
coincidence. Mlle. Dorian was, therefore, an accomplice of a murderer.

Stuart sighed. He would have given much--more than he was prepared to
admit to himself--to have known her to be guiltless.

The identity of the missing cabman now engaged his mind. It was quite
possible, of course, that the man had actually found the envelope in
his cab a was in no other way concerned in the matter. But how had
Mlle. Dorian, or the person instructing her, traced the envelope to
his study? And why, if they could establish a claim to it, had they
preferred to attempt to steal it? Finally, why all this disturbance
about a blank piece of cardboard?

A mental picture of the envelope arose before him, the number, 30,
written upon it and the two black seals securing the lapels. He paused
again in his walk. His reflections had led him to a second definite
point and he fumbled in his waistcoat pocket for a time, seeking a
certain brass coin about the size of a halfpenny, having a square hole
in the middle and peculiar characters engraved around the square, one
on each of the four sides.

He failed to find the coin in his pocket, however, but he walked
briskly up a side street until he came to the entrance to a tube
station. Entering a public telephone call-box, he asked for the
number, City 400. Being put through and having deposited the necessary
fee in the box:

"Is that the Commissioner's Office, New Scotland Yard?" he asked.
"Yes! My name is Dr. Keppel Stuart. If Inspector Dunbar is there,
would you kindly allow me to speak to him."

There was a short interval, then: