continuation in a fine scratch in the paint of the floor. Muller
followed up this scratch and it led him over towards the window and
then back again in wide curves, then out again under the desk and
finally, growing weaker and weaker, it came back to the neighbourhood
of the pool of blood, but on the opposite side of it. Muller got
down on his hands and knees to follow up the scratch. He did not
notice the discomfort of his position, his eyes shone in excitement
and a deep flush glowed in his cheeks. Also, he began to whistle
softly.

Joseph Muller, the bloodhound of the Austrian police, had found a
clue, a clue that soon would bring him to the trail he was seeking.
He did not know yet what he could do with his clue. But this much
he knew; sooner or later this scratch in the floor would lead him
to the murderer. The trail might be long and devious; but he would
follow it and at its end would be success. He knew that this scratch
had been made after the murder was committed; this was proved by the
blood that marked its beginning. And it could not have been made by
any of those who entered the room during the day because by that
time the blood had dried. This strange streak in the floor, with
its weird curves and spirals, could have been made only by the
murderer. But how? With what instrument? There was the riddle
which must be solved.

And now Muller, making another careful examination of the floor,
found something else. It was something that might be utterly
unimportant or might be of great value. It was a tiny bit of
hardened lacquer which he found on the floor beside one of the legs
of the desk. It was rounded out, with sharp edges, and coloured
grey with a tiny zigzag of yellow on its surface. Muller lifted it