That afternoon Muller passed through Horn's office with a bundle
of papers, on his way to the inner office occupied by his patron,
Chief of Police Bauer. Horn, who had avoided Muller since yesterday
although he was conscious of a freshened interest in the man, raised
his head and watched the little detective as he walked across the
room with his usual quiet tread. The commissioner saw nothing but
the usual humble business-like manner to which he was accustomed
- then suddenly something happened that came to him like a distinct
shock. Muller stopped in his walk so suddenly that one foot was
poised in the air. His bowed head was thrown back, his face
flushed to his forehead, and the papers trembled in his hands. He
ran the fingers of his unoccupied hand through his hair and murmured
audibly, "That dog! that dog!" It was evident that some thought
had struck him with such insistence as to render him oblivious of
his surroundings. Then he finally realised where he was, and walked
on quickly to Bauer's room, his face still flushed, his hands
trembling. When he came out from the office again, he was his usual
quiet, humble self.

But the commissioner, with his now greater knowledge of the little
man's gifts and past, could not forget the incident. During the
afternoon he found himself repeating mechanically, "That dog - that
dog." But the words meant nothing to him, hard as he might try to
find the connection.

When the commissioner left for his home late that afternoon, Muller
re-entered the office to lay some papers on the desk. His duties
over, he was about to turn out the gas, when his eye fell on the
blotter on Horn's desk. He looked at it more closely, then burst