that
particular shop was a very brisk one; scores of people had bought
note-paper there, similar to that on which the supposed doctor had
written his tricky letter. The handwriting was cramped, perhaps a
disguised one; in any case, except under very exceptional circumstances,
it could afford no clue to the identity of the thief. Needless to say,
the tramp, when told to write his name, wrote a totally different and
absolutely uneducated hand.

"Matters stood, however, in the same persistently mysterious state when
a small discovery was made, which suggested to Mr. Francis Howard an
idea, which, if properly carried out, would, he hoped, inevitably bring
the cunning burglar safely within the grasp of the police.

"That was the discovery of a few of Mr. Knopf's diamonds," continued the
man in the corner after a slight pause, "evidently trampled into the
ground by the thief whilst making his hurried exit through the garden of
No. 22, Phillimore Terrace.

"At the end of this garden there is a small studio which had been built
by a former owner of the house, and behind it a small piece of waste
ground about seven feet square which had once been a rockery, and is
still filled with large loose stones, in the shadow of which earwigs and
woodlice innumerable have made a happy hunting ground.

"It was Robertson who, two days after the robbery, having need of a
large stone, for some household purpose or other, dislodged one from
that piece of waste ground, and found a few shining pebbles beneath it.
Mr. Knopf took them round to the police-station himself immediately, and
identified the stones as some of his Parisian ones.

"Later on the detective went to view the place where the find had been
made, and there conceived the plan upon which he built big cherished
hopes.

"Acting upon the advice of Mr. Francis Howard, the police decided to let
the anonymous tramp out of his safe retreat within the station, and to
allow him to wander whithersoever he chose. A good idea, perhaps--the
presumption being that, sooner or later, if the man was in any way mixed
up with the cunning thieves, he would either rejoin his comrades or even
lead the police to where the remnant of his hoard lay hidden; needless
to say, his footsteps were to be literally dogged.

"The wretched tramp, on his discharge, wandered out of the yard,
wrapping his thin coat round his shoulders, for it was a bitterly cold
afternoon. He began operations by turning into the