"Calm night."

Three times, over five thousand miles of air, this great voice bellowed
its message.

The silence which followed was ghostly. Cold perspiration stood out on
Curlie's brow.

It was not necessary for him to calculate the location from which this
message was sent. He knew that it had come from the hotel. And it had.

"Next thing," he told himself with a groan, "the International Service
will be on my back for letting that lion roar. I ought to turn that over
to the police; but I won't, not just yet."

CHAPTER V

IN THE DARK

As the clock in a distant college tower struck the hour of eleven the
following night, a flat looking car with a powerful engine stole out
into the road that ran by the Forest Preserve. It was the Humming Bird.
Joe Marion was at the wheel. Curlie sat beside him.

On the back of the car was a miscellaneous pile of instruments all
securely clamped down. Above there hung suspended between two vertical
bars a square frame from which there gleamed the copper wires of a coil.

To catch a radiophone on wheels, Curlie had reasoned, one must mount his
radio compass on wheels and pursue the offender. How well it would work,
he could not even guess, but anything was better than sitting there
helpless in the secret tower room listening to this person tearing up
the air in a manner both unwise and unlawful.

So here they were, prepared to make the test.

"Of course," Curlie grumbled, "now we've got the trap set, the ghost may
decide not to walk on this particular night. That'll be part of our
rotten luck."

"Most ghosts, I'm told," chuckled Joe, "prefer to walk when there's
someone about, for what's the good of a ghost-walk when there's no one
to see. So our radio ghost may show up after all."

Curlie lapsed into silence. He was reviewing the events which led up to
this thrilling moment. When the message on 600 came banging to his ears
with great power on that first night, he had carefully platted the
various locations of the person who had sent the messages. There had
been some criss-crosses shown but, in the main, a line drawn through
these points had formed an oblong which on the actual surface of the
ground must have been some ten miles in length by six in width. One
interesting point was that the first and last messages of that night had
been sent at points not a quarter of a mile apart.

"Which goes to show," he reasoned, "that this fellow started from a
certain poi