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 and 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 pieced of cardboard?