found an opportunity for proving their worth in the rescue of pretty Bessie Gleason and her mother from an old chateau in Lorraine where Carl Potzfeldt, a German spy, had them imprisoned. These interesting and exciting events will be found in the second volume of the series, entitled: "Air Service Boys Over the Enemy's Lines; or, The German Spy's Secret."
Then came another series of happenings that must always appeal to boy readers fond of thrilling scenes, for in the next book, among many other things, is told how Tom and Jack succeeded in silencing the monster cannon that from a distance of sixty miles and more was bombarding Paris. That will be found narrated in "Air Service Boys Over the Rhine; or, Fighting Above the Clouds."
Then there is the volume just preceding this, in which again the two brave young Yankee air pilots were given an opportunity to prove the value of their training, now in the service of the American forces, for General Pershing had come across the sea, and his army was beginning to make its presence felt at several sectors of the battleline.
What they saw and did, as well as vivid descriptions of the momentous events accompanying the great German drive is told in the fourth book