“What are you doing?” I asked.  “You heard what she said.”

“One thing you can be certain of,” he answered, “that despatch can never be stolen or tapped by spies.”

“Why—­what is this?” I asked, pointing to the instrument.

“The invention of Major Squier, of the army,” he replied, “by which any number of messages may be sent at the same time over the same wire without the slightest conflict.  Really it consists in making wireless electric waves travel along, instead of inside, the wire.  In other words, he had discovered the means of concentrating the energy of a wireless wave on a given point instead of letting it riot all over the face of the earth.

“It is the principle of wireless.  But in ordinary wireless less than one-millionth part of the original sending force reaches the point for which it is intended.  The rest is scattered through space in all directions.  If the vibrations of a current are of a certain number per second, the current will follow a wire to which it is, as it were, attached, instead of passing off into space.

“All the energy in wireless formerly wasted in radiation in every direction now devotes itself solely to driving the current through the ether about the wire.  Thus it goes until it reaches the point where Whiting is—­where the vibrations correspond to its own and are in tune.  There it reproduces the sending impulse.  It is wired wireless.”

Craig had long since finished sending his wired wireless message.  We waited impatiently.  The seconds seemed to drag like hours.

Far off, now, we could hear a whistle as a train finally approached slowly into our block, creeping up to see what was wrong.  But that made no difference now.  It was not any help they could give us that we wanted.  A greater problem, the saving of one man’s name and the re-establishment of another, confronted us.

Unexpectedly the little wired wireless instrument before us began to buzz.  Quickly Kennedy seized a pencil and wrote as the message that no hand of man could interfere with was flashed back to us.

“It is for you, Walter, from the Star,” he said, simply handing me what he had written on the back of an old envelope.

I read, almost afraid to read: 

Robbery story killed.  Black type across page-head last edition,
“Treasure-train safe!”
     McGRATH.

“Show it to Miss Euston,” Craig added, simply, gathering up his wired wireless set, just as the crew from the train behind us ran up.  “She may like to know that she has saved her father from himself through misunderstanding her lover.”

I thought Maude Euston would faint as she clutched the message.  Lane caught her as she reeled backward.

“Rodman—­can you—­forgive me?” she murmured, simply, yielding to him and looking up into his face.

II

THE TRUTH DETECTOR