ng? Oh, this is Inspector Dunbar. You called me up here at the
Yard a few moments ago, did you not? Correct, doctor; that's all I
wanted to know. I am coming now."

"Good," said the Assistant Commissioner, nodding his approval. "You
will have to check 'phone messages in that way until you have run your
mimic to earth, Inspector. I don't believe for a moment that it was
Sergeant Sowerby who rang you up at Dr. Stuart's."

"Neither do I," said Dunbar grimly. "But I begin to have a glimmer of
a notion who it was. I'll be saying good-night, sir. Dr. Stuart seems
to have something very important to tell me."

As a mere matter of form he waited for the report of the constable who
had gone in quest of Sowerby, but it merely confirmed the fact that
Sowerby had left Scotland Yard over three hours earlier. Dunbar
summoned a taxicab and proceeded to the house of Dr. Stuart.

CHAPTER VII

CONTENTS OF THE SEALED ENVELOPE

Stuart personally admitted Dunbar, and once more the Inspector found
himself in the armchair in the study. The fire was almost out and the
room seemed to be chilly. Stuart was labouring under the influence of
suppressed excitement and was pacing restlessly up and down the floor.

"Inspector," he began, "I find it difficult to tell you the facts which
have recently come to my knowledge bearing upon this most mysterious
'Scorpion' case. I clearly perceive, now, that without being aware of
the fact I have nevertheless been concerned in the case for at least
a week."

Dunbar stared surprisedly, but offered no comment.

"A fortnight ago," Stuart continued, "I found myself in the
neighbourhood of the West India Docks. I had been spending the evening
with a very old friend, chief officer of a liner in dock. I had
intended to leave the ship at about ten o'clock and to walk to the
railway station, but, as it fell out, the party did not break up until
after midnight. Declining the offer of a berth on board, I came ashore
determined to make my way home by tram and afoot. I should probably
have done so and have been spared--much; but rain began to fall
suddenly and I found myself, foolishly unprovided with a top-coat, in
those grey East End streets without hope of getting a lift.

"It was just as I was crossing Limehouse Causeway that I observed, to
my astonishment, the head-lamps of a cab or car shining out from a dark
and forbidding thoroughfare which led down to the river. The sight was
so utterly unexpecte