river when the
searchlight flashed from the gray prowler; was there, Mike?"

"Not even a cork," said Mike.

"Well, anyway, that clears youse guys," grunted the leader. "Now you
better beat it."

Bidding Hanada good night, Johnny walked across the bridge, around four
blocks, then made a dash for his room. There was dust on his blankets,
but he could shake it off. Anyway, he probably would not sleep much that
night. Probably he would spend most of the night sitting by the window,
listening to the lap of the waters of the old river and trying to solve
the strange problem of the bullets fired apparently from the depths of
the stream.

CHAPTER XV

THE CAT CRY OF THE UNDERWORLD

Dodging in front of a street car, Johnny turned abruptly to the right
and trailed a taxi for half a block; then he shot across the sidewalk to
the end of a dark alley. Then he flattened himself against the wall and
listened. Yes, it came at last, the faint thud of cautious footsteps. He
had not thrown the man off the scent.

"Well then, I will," he muttered, gritting his teeth. Johnny was a
trifle out of sorts to-night. The chase annoyed him.

He dodged down the alley, then up a narrow court. Prying open the window
of an empty building, he crept in and silently slid the sash back in its
place. Tiptoeing across the hall with the lightness of a cat, he crept
up the dusty stairs. One, two, three flights he ascended, then feeling
for the rounds of a short ladder, he climbed still higher, to lift a
trapdoor at last and creep out upon the roof.

Once there he skulked from chimney to chimney until he had crossed the
flat roofs of three buildings. The third had a trapdoor close to a
chimney. This he lifted, then dropped behind him. He was now in his own
building. Panting a little from the exertion, he tiptoed down the hall,
turned the key and entered his room.

Having made sure that the iron blinds were closed, he snapped on a
light. His eyes, roving around the room, fell presently upon something
white on the floor. Johnny could see his own name scrawled upon it.
There were but a few people in all the world who knew that Johnny
Thompson had ever lived here. Probably all of those who did know thought
him dead and buried in Russia. Who had written this note? Friend or foe?

He tore open the envelope and glanced at the note. It came to the point
with brutal frankness.

"Johnny Thompson: You are known to have in your possession rare gems
w