and her mother, but Jack, who was more than casually interested in
the girl, was suspicious of this man. And his suspicions proved
correct, for Potzfeldt had planned a daring trick.

After some strenuous happenings, in which the Air Service Boys
assisted, Bessie and her mother were rescued from the clutches of
Potzfeldt, and went to Paris, Mrs. Gleason engaging in Red Cross
work, and Bessie helping her as best she could.

Immediately preceding this present volume is the third, called "Air
Service Boys Over the Rhine; or Fighting Above the Clouds."

By this time the United States had entered the great war on the side
of humanity and democracy.

Then the world was startled by the news that a great German cannon
was firing on Paris seventy miles away, and consternation reigned
for a time. Tom and Jack had a hand in silencing the great gun, for
it was they who discovered where it was hidden. Also in the third
volume is related how Tom's father, who had disappeared, was found
again.

The boys passed through many startling experiences with their usual
bravery, so that, when the present story opens, they were taking a
much needed and well-earned rest. Mr. Raymond, having accomplished
his mission, had returned to the United States.

Then, as we have seen, came the news of the arrival of the first of
Pershing's forces, and with it came the sad message that Harry
Leroy, the chum of Torn and Jack, had fallen behind the German