without the United
States knowing anything about it. Once again a heavy responsibility
was thrown upon our Secret Service. How did they carry it?

We have already seen that the Service had its agents in the most
unsuspected places. One of the most unsuspected of them all must have
gotten to work, for within a week the Service knew that something
unusually mysterious was going on inside the German Embassy. Patiently
the resourceful agents worked and worked, bit by bit, until at
last--they won. They secured the most necessary document of the whole
case, the one which Germany was most anxious to keep secret. When it
was made public, it caused the greatest sensation of years. Here it
is:--

"Berlin, January 19, 1917.

(To von Eckhardt, the German Minister in Mexico.)

"On the first of February we intend to begin submarine warfare
unrestricted. In spite of this it is our intention to endeavor to keep
neutral the United States of America.

"If this attempt is not successful, we propose an alliance on the
following basis with Mexico: that we shall make war together and
together make peace. We shall give general financial support, and it
is understood that Mexico is to recover the lost territory in New
Mexico, Texas, and Arizona. The details are left to you for settlement.

"You are instructed to inform the President of Mexico of the above in
greatest confidence, as soon as it is certain that there will be an
outbreak of war with the United States, and suggest that the President
of Mexico on his own initiative should communicate with Japan,
suggesting adherence to this plan. At the same time offer to mediate
between Germany and Japan.

"Please call to the attention of the President of Mexico that the
employment of ruthless submarine warfare now promises to compel England
to make peace in a few months."

"Zimmermann."

Alfred Zimmermann was the German Foreign Minister.

The German defense to this piece of absolute proof was what we have
since learned to expect from Germans;--

"We were not doing it. And anyway, it was not unfriendly, and we had a
perfect right to do it."

The once great German machine was now without its leaders, and all it
could do was to carry on a number of small local agitations, with no
directing intelligence. A very few months after the publication of the
Zimmermann letter, the United States itself went into the war. Then
the constant struggle between detectives and enemy-a